I can understand that some people don't want to deal with changing keyboards even if they don't want to be tracked. But you are literally here asking about keyboards. If this is not the place to talk about this then what is? Anyone interested enough to wonder about what keyboard they use should consider their privacy as the main aspect for a keyboard, as it is an app that can see everything you write, including passwords.

but the reality is most foss apps are far inferior user experiences to corporate apps

This is absolutely wrong and too often repeated as a mantra, and not because they have actually good UX, but because the corporate apps have it worse even (but they set the standard so anything that isn't like theirs is bad). From all keyboards I have tried (many, including corporate ones, closed source, etc) the closed source ones have usually the worse UX. They start better and then worsen over time. You said you like the personalisation options, but often there's less options in any closed source corporate keyboard. It took them years for gboard to actually let users have the number row always on top. I could have that in other keyboards long before gboard. Swiftkey was wonderful, but over the years it got so bloated that it lagged when used. There's unfortunately not a perfect keyboard, but through all the posts in this thread there were a lot of good recommendations that allow you to choose good customisability, respect of user privacy, and also fringe use cases not often supported. And in general, the worse options are the closed source ones.

The only real downside of Foss keyboards is that as they have more options they usually require a bit more set up time which puts many people off.

I'm currently using Heliboard, lots of customisability, Foss, good language support and a must for me, multi language support. So far I am making less typos than with many other keyboards. The downside is no swipe support right in the app, but you can get it to work too if interested using 3rd party libraries.

In the past I've been using gboard which was OK for a while but started making more and more typos and wrong corrections over time, that plus trying to degoogle myself pushed me away.

Also anysoft keyboard, pretty nice, and was quite happy with it but again started getting tired of some typos I kept making.

I am keeping an eye on futo keyboard too, which at the moment doesn't support multi language support, maybe in the future when implemented I'll try it.