People no longer double-space after sentences.  No one cares that further compares metaphorical distance and farther compares physical distance.  Most people seem to think that joining two independent clauses with a comma (a comma splice) is just fine.  Things are now done on accident instead of by accident.  Compute used to be something you did; now, it's something you rent.  People seem to have given up on less being used for uncountable things and fewer for countable things.  Now they just use less for everything.  People these days are enamored 'by' something instead of with it (or of it, for our British friends).

Pour one out for the Oxford Comma .

Let's eat Grandma

Commas save lives!

Ain't ain't a word.

It is now.

Unique coming to just mean unusual.

Ending sentences with propositions, and getting them jumbled around. My work does it in their advertisements and i cry every time.

"See what classes you can register for." Or modifying it to be worse; "see what classes you can register for fast"

Apple put the nail in the coffin for adverbs when "Think different" let illiterates think they were speaking correctly.

Not exactly what you're asking, but double spaces after ends of sentences.

"Reticent" used to mean 'reluctance to speak', or, 'holding your tongue', but in the last decade I saw it being used more frequently as a straight up synonym for 'reluctance'. I wonder if people maybe think it's a more authoritative sounding word?

It's not a change of convenience or cultural drift, just a sign of people reading less and subconsciously trying to hide it, I think.

The one that bothers me most (heard a lot in the software dev world) is when people say process-eez instead of processes, even if it is technically a word now, like ain’t

Literally and Crescendo are my vocabulary pet peeves. Both have stupidly evolved to include definitions that mean the exact opposite of their true meanings.

Literally is annoying, but Crescendo is impossible. That is a specific musical term with an unalterable meaning. It means a gradual increase in volume, but it has come to mean a climax. Something will be described as "it rose to a crescendo," and that is simply wrong. Something can crescendo to a climax, but not the other way around. If you change it to mean the climax, you can't crescendo to a crescendo, s what's the word for gradually increasing the volume?

Besides, it's a musical term, and musicians will define musical terms, not illiterate civilians.

And if Literally can also mean "similar to," then what word can be used to literally mean Literally?

I was one of the first years to have the new spelling rules.
It used to be, that a letter appearing more than twice in direct sequence would be cut to just twice. But that was lifted and is now just how many it should normally be. Examples: Schifffahrt, Brennnessel, Seeelefant.

It used to be, that "dass" could also be spelt "daß", but the rules for "ss" and "ß" were made clearer and more concise.

They also changed the way words could be split at the end of a line. If there was a double consonant in-between the syllables that were to split, the first syllable would take both consonants but now they are split evenly.
immer is split im-mer and not imm-er
But ck makes an exception: knackig is kna-ckig instead of old knak-kig