I've spent some time today trying to come up with a conclusive answer to your question, thinking back on what has and hasn't worked over the years. Here's the result.

The tech activist's guide to persuasion

The following guide is a collection of principles that may help a tech activist grab people's attention and convince them to make more ethical choices with regard to the technology and platforms they use. If, at times, they may sound mutually exclusive and contradictory, that's because they are. But then again, so are the people they pertain to.

• Keep the user in mind: people use tech because it's a tool that helps them reach their goals. Hence, make sure you first know their use case and level of expertise and only then decide if and which alternative tool to suggest. Trying something new is a big ask in and of itself; don't ruin that opportunity by suggesting tools that people either cannot handle or that aren't helpful to them.
• Call out big tech where you can: by enshittifying each and every single one of their products, it has become incredibly easy to show the average user how careless, incompetent, if not outright malicious big tech corporations act. Call them out on their behaviour wherever you see it. Make people aware how little they are 'owners' of a Windows machine when Microsoft can just remotely change settings, force online accounts or break their machines by pushing poorly-tested updates. Make them question how much Facebook helps them connect with friends when all they see there is an algorithmically-driven hellscape of ads and artificially pushed content they didn't ask for. Call into question the utility of Amazon when pages 1 through 100 are full of sponsored content and cheaply-made crap straight out of China, none of which the manufacturer will be accountable for when they inevitably fray, break or dissolve only months after purchase. Don't be a dick and go on a long-winded rant about the "evil corpos", though. Just drop a tidbit of frustration, and let the slow poison do its work. Once you hear somebody say, "Well, what do you suggest?", that opens up a different kind of conversation which may lead to transition.
• Stress the added value of your solution: as much as we may see intangibles like privacy, control and independence as valuable, we must accept that some (many? most?) people do not share that view. Therefore, advertising an app like, say, Newpipe (an alternative YouTube frontend) as "privacy-friendly" may not mean much to the average consumer. Instead, stress the value the app adds to people's lives: "Do you want to get rid of unskippable mid-video ads thanks to the built-in adblocker? Subscriptions and playlists without having to log in to Google? Background playback and audio/video downloads?" Now you've got somebody's attention.
• Only contribute value to known good platforms: Yes, I just called you valuable without even knowing you. But you are likely providing value to other people's lives in many different ways: maybe you're a passionate hobbyist, showing off your crafty projects online and inspiring others to follow in your footsteps. Maybe you're a skilled techie providing friends and family with remote support whenever something breaks. Maybe you've just become a parent and the rest of the family wants to get updated with cute pics of your kids. Or maybe you're just a particularly pleasant person that people want to talk to. Whatever the value you provide to others may be, by making this value accessible through known bad platforms, you are increasing the value of those platforms and making it even harder for others to leave them. Why not make it known that from now on, you will no longer show off your projects on Instagram, but on a platform that respects both you as a creator and your followers? Why not ask people to install RustDesk instead of Teamviewer for remote support? Why not let people know that those cutesy pictures of the kids will be shared with everyone interested, but exclusively on a privacy-friendly messenger such as Signal, and people are welcome to join the new family group chat there? If you can, throw your weight and your value behind something that values you, and you might just be able to pull people along with you.
• Share your enthusiasm, not your gloom: with the way our media works (and maybe our psyche), it's easy to get bogged down in doom and gloom, solely focussing on all the evil shit tech corporations do and how we must protect ourselves from them. That's not how you inspire people, though. Therefore, where the opportunity presents itself, share your enthusiasm for the awesome solutions you have discovered and implemented. Do tell people about that amazing FOSS app that can bake pancakes and shits rainbows. Show them that self-hosted music server that you've set up and that has allowed you to cancel your Spotify subscription for good. Share your appreciation for your new Linux system which breathed new life into a notebook that Microsoft deemed ripe for the scrapyard. They'll not necessarily want to adopt any of the solutions you're presenting to them that very same day, and that's OK. But they will have "heard good things" about something that, up to that point, they didn't know even existed. And once the time is ripe for them, they'll come to you for guidance.

Chat apps are actually one of the hardest problems because they're subject to severe network effects - why move to a platform where most of your social network isn't?