I'd say the The Expanse fits the bill. It is a book series with a very successful television adaptation.

civilizations, diplomacy, and exploration

Babylon 5 - It has a bit of a slow start with the first season (just the 1990's Trek shows), but it picks up about midway through season 1 and gets progressively better (higher stakes) until season 4. Season 5 is okay, and then there are series of movies, and recently even an animated show in the universe.

Babylon 5 and Farscape are great.

Babylon 5 is more like Trek with diplomacy and semi-realisitic plots, while Farscape leans a bit more toward Star Wars; fun, campy, weird at times but well-written.

You may also like Red Dwarf which is like the IT crowd, but in space.

I mean, the Expanse is fantastic sci fi, both book and show. It's not that Star Trek like though.

In particular I really like the episodes that deal with interacting with other civilizations, diplomacy, and exploration more-so than say, an anomaly episode.

In light of this, and since you were able to work through the not-so-stellar episodes of ST, I'd strongly argue that Babylon 5 should be your next stop.

It has a slow start, some more mixed episodes, dated special effects and both main characters (they switched after season 1) are plain "heroic American leader" types, but virtually everything else is top tier even today. An excellent political plot, humor, great characters with genuine growth.

Just be aware that it is different from DS9 (personally, I like both).

Battlestar Galactica (the new one) and The Expanse are probably worth pointing out, too. To me, they're the best high-production-value sci-fi shows that didn't sacrifice their plot. Nevertheless, both are far more grim than the shows you've mentioned and overall "feel" different.

For All Mankind is the Star Trek prequel we should have had. Co-created by Ron Moore (Deep Space Nine, Battlestar Galactica), the show has a bunch of Trek alumni working behind the scenes. It features human drama (and sometimes melodrama), geopolitical diplomacy, sweeping cultural change and scientific adventure against the backdrop of a multi generational future history, starting with the first moon landing.

The other science fiction series that I feel most-closely mimic the energy of Star Trek:

• Star Gate SG1/Atlantis - Episodic planetary exploration and adventure with overarching serial universe-building
• Babylon 5 - Space politics and looming galactic war (the show pitched to Paramount right before they made Deep Space Nine)
• The Orville - Space utopia and moral dilemma seen from the outside (The Next Generation with all the funny outtakes left in)

(This list is for anyone reading. Enjoy B5, OP! Let us know when you get to that part where everyone cries.)

The Expanse is an amazing sci-fi series that just gets better every season. Politics, war, discovery of new life, all within new civilizations cataloguing the early expansion of humans from the Earth to within our local system. Acting is top tier, graphics get better each season due to it's meteoric rise in popularity.

But yeah, nothing quite like those pure gold episodes of Star Trek: TNG. The new Star Trek: Strange New Worlds is more like TNG than the other series going on right now, but only has 2 seasons at this point I believe.

If you like British comedy then Red Drarf was surprisingly good imo

I don't know if you gave Stargate Atlantis a try. It doesn't reach the heights of SG1, but it has it's moments and is enjoyable overall.

The obvious answers are outside TV media.

Mass Effect 1, the video game, was originally conceived as a Star Trek game, but they couldn't secure the IP rights, so ended up pivoting to a new universe that feels Star Trek like. Play it on story mode.

In print, there are literally a hundred reasonable options, some more or less like different elements of Trek. A good choice (in my opinion) is The Spiral Wars -- rogue ship and crew, diplomacy, great combat, alien civilizations that are non-monolithic... Or CJ Cherryh's Alliance Union universe (a good entry point is Downbelow Station, a good overview of the universe) -- many different scenarios and topics and a lot of ethical dilemmas that would make Trek proud.

Of course, if TV is your thing, try out Babylon 5, Stargate, or Farscape. They all sort of start slow.

Highly recommend the Culture Novels by Iain M Banks. They're not necessarily family friendly due to some adult themes and moments, but diplomacy, exploration and intrigue are the main focuses with a bit of action sprinkled in.

... (or maybe some books)...
.

Then how about the Bobiverse series? That should fit the bill perfectly. Even has a Riker! I'm a big fan of the audio books.

And definitely Project Hail Mary as a one off.

And maybe Expeditionary Force. That one is a bit much militaristic for my taste but I got to love the audio books anyways.

I don't understand, aren't you supposed to start it all over again from the beginning and continue until your death? Are you allowed to watch ST just once?

We just watched Scavenger's Reign, If exploration is your thing. Not much diplomacy there tho

I haven't seen Battlestar Galactica mentioned here. Great sci-fi show, although there is pretty much no alien life to speak of. Instead it's a juggling act between humans and the robots they created, in space. I'd almost say it's a long-form version of Blade Runner, where the robots actually beat humanity and forced them to run from Earth for survival.

If you want something that's in the vein of episodic sci fi and is family friendly, try find Seaquest DSV.

In that same vein again, i would recommend Andromeda as it was created by Gene Roddenberry but the lead was Kevin Sorbo who had gone full maga mode, so maybe pirate that one 😁

Edit: did you also watch all of Stargate Atlantis & Universe?

If you like reading leftist utopian sci-fi, it doesn't get much better than The Culture series by Iain M. Banks. It gets dark though!

I've mention a couple of shows in some replies but thought of some others so ill but them all here for both of our convenience

Based on this part of what you were asking fyi.

I really like the episodes that deal with interacting with other civilizations, diplomacy, and exploration more-so than say, an anomaly episode.

Space oriented

Firefly

Farscape

Lexx (maybe i didnt watch it, just caught some episodes here and there memory is foggy)

If you like the idea of a show about just the startrek episodes where they go back in time to various points in earth history and especially alternate earth history then i have the perfect show for you Its very similar to stargate in set up but not at all the same show

Sliders (this one and firefly are my top 2 picks for episodic style shows)

Honorable mentions

for just good space sci fi but more drama driven

Space: Above and Beyond

Battlestar Galactica (I never saw the original so cant recommend it)

Babylon 5

Maybe even Doctor Who? And Torchwood (these might be getting a bit off topic now)

For novels, i would recommend

Battletech books¹

¹read in chronological order. The universe of battletech has a big time scale all the collected stories take place over. You do get some spoilers here and there but i think not knowing what events took place ready when the authors wrote their book adds some good flavour to the overall experience

Doctor Who is essentially Britain's louder Star Trek.

@darthelmet

Blake's 7: 70s BBC, cheesy FX, some great acting and a largely unprincipled crew which is fun.

Space 1999: if you had enjoyed TOS more you would love this: outlandish 70s episodic antiphysics

Vagrant Queen: space opera SyFy show that's pretty funny. Some blood, one season

Andromeda: Season 1 is okay

Babylon 5 is the show you're looking for :)

The Expanse is the best sci-fi TV show in recent memory. Though it's not really close to Star Trek.

I don’t see Firefly mentioned yet. Also if you liked TOS, try the 70’s Buck Rogers.

Not quite what you wanted, but the Alien Nation TV series is pretty good, if you don't mind a little buddy cop drama in your science fiction.

There's so much modern Trek at this point I don't even know if that's necessary.

Anyway, I'd say I see a ton of overlap between liking Trek and liking The Expanse, although it's more political and less "alien of the week diplomacy". Still, it goes places, give it a look.