I'm upgrading because my phone is losing (lost?) support. I use a OnePlus 7 Pro and love it and wouldn't bother upgrading otherwise. I'd appreciate some recommendations of android phones you like, please.
You could install LineageOS on your existing phone instead of upgrading. The OnePlus 7 Pro is supported. The install process can be daunting depending on your technical skills, but it's a one-time process since the phone gets updates over-the-air after the OS is installed.
I did this with my OnePlus 6 a few months ago and the experience has been good. Switching to LineageOS bumped Android to version 13, whereas it was stuck on Android 11 on stock OnePlus firmware. I'm getting regular updates again, including open-source Android security patches. Not everything gets patched though, some of the core firmware is proprietary to OnePlus and that cannot be patched by anyone but them. It's letting me extend the life of a phone still works well and has a 3.5mm headphone jack.
Really seconding this. A lot of guides are also available with videos and OnePlus is notorious for being easy to unlock and flash.
The op7pro is still a good device and if you have kept it till now you might as well give it a breath of fresh life by installing a new Android version.
If one is okay with rooting and can get a (non Verizon) Google pixel, graphene OS is for the OCD fanatics, and CalyxOS is a more featured runner up.
Both are only on pixels largely for the re-lockable boot loader.
lineage is also a good rom, and they support way more devices