Personally, I don't trust Android and all the crap installed in it at all. So, I do very limited secure activities on my phone. I have never logged into my email on my phone, for instance [1]. The only thing private is messenger apps, which is an unfortunate minimum requirement on social life. Always looking for a way out.

[1] Also because I deal with work on my own time.

I use Simple Keyboard (based on the AOSP keyboard), which is a very basic FOSS keyboard with no logging, suggestions or any of that. Other good options with more features most people want are OpenBoard and AnySoft. Hacker's Keyboard is a decent one too.

Related question: Does anyone have any suggestions for an OSS keyboard with suggestions and (good) swipe functionality? I currently use Gboard and it's great, but, well, it's a Google product.

The FOSS keyboard with the best swipe functionality is AnySoft. But it is miles behind SwiftKey and Gboard in my experience. With some patience and training it is serviceable though.

This is why I stick with SwiftKey. Nothing beats it, and although it got bought by Microsoft, they did not Frankenstein it. If you look for the app start with the 'M' of Microsoft though.

Yeah, I think SwiftKey with a firewall blocking outgoing requests is the most feature-rich keyboard experience on Android which isn't outrageously privacy invasive

Personally, I still like using Simple Keyboard. It's the complete opposite of something like Swiftkey. does one thing and does it well, is super light too.