Anything compatible with Graphene OS (https://grapheneos.org/); a second-hand Pixel will work best, if you can find one cheap. I use it as my daily driver on a Pixel 7a and it's great; it's the most stable and easiest-to-install custom ROM I've ever used, and I've been rooting my Android devices for over a decade now.
So my Fairphone is not supported because the security updates aren't good enough. Serves me right trying to find an ethical approach to mobile computing.
I understand GrapheneOS' philosophy but buying a google product to get away from google software is certainly... a choice. Refurbished or not buying a Pixel would serve Google's interests, nevermind the fact that I bought my current phone a couple years ago hoping to get close to a decade of use out of it.
Realistically software freedom on mobile phones is doomed until the industry improves the firmware situation. Every project suffers from severe drawbacks because of it.
It doesn't have the worst of google apps, but it still runs Play Services with all its opaqueness and potential spyware. So Gemini should hopefully not be an issue but GrapheneOS would still be nice to have.
If you want to keep your Fairphone and ditch android, Fairphone 4 and 5 both appear to be well supported by Ubuntu Touch. The downside is that Ubuntu Touch is currently still based on the 2020 LTS release of Ubuntu (which does still get updates, at least). Fairphone 4 is also somewhat supported by postmarketOS, but call support there is listed as "partial".
I hear you! Hardware fragmentation is a serious issue, very difficult to deal with as a small team, so I can't hold it against them, but I really wish I had been able to put it on my old Note 9 instead of buying a Pixel 😑 (doesn't have to be a Pixel, there are other supported devices, but it's easiest and works best)
Have you tried CalyxOS (https://calyxos.org/)? Review from a year ago seems pretty good (fair warning: Reddit link). I'm keeping Calyx in my back pocket in case Graphene goes tits up.
Yes, I've used all my apps pretty seamlessly. I had to turn on "exploit protection compatibility mode" for some of them like banking, but they work fine. You can get Google Play, and it runs in a sandbox, but I use Obtainium and Aurora Store (Aurora in particular would be of interest to you, it's just a frontend for the Google Play store which allows anonymous connections: https://f-droid.org/packages/com.aurora.store/). I moved to Aegis for my 2FA because I was looking for a way out of the Twilio/Authy ecosystem. I don't play games on my phone, so I can't report back on how those work.
Can't even get on the bus or easily apply for government programs/loans, or review your medical anything online without an app now in my province. There's workarounds but they are not accessible.
At least with Google they don't make the cornerstone of their branding lies (we are super focused on YOUR privacy), and you actually have some choice in how you use your phone.