You can research a phone you like and check if it has an unlockable bootloader, root it, and install something like LineageOS on it. It's fairly straight-forward, not super technically demanding, but it does require some tinkering and time setting up.

xdaforums.com is where the rooting kids hang out, post guides for specific models, upload images et c, you can probably do it in an afternoon with GPT.

The issue is that some apps, notably banking and official type apps, usually don't work as they rely on google services for operation. I solve it by having a cheap secondary phone that I only use for that stuff.

Oh, I almost forgot: FUCK YOU GOOGLE