I feel the 50 years support claims, whether in hardware or software, should be of little concern; you'll grow tired of it, no one is going to rock the same phone for 10 years, replacing components as they fail and whatever Fairphone's delusion is.

as to concrete recommendations, take a look at Xiaomi phones (Mi/Redmi/Poco/etc.). they ship with a bloated spyware called MIUI which is such a horrific mess on so many levels I can't begin to count the ways it sucks. even moderately competent phones have trouble keeping up with the bloat, they glitch out, drop frames, freeze, etc. so people just get rid of them and upgrade to something snappier. as a consequence, they can be had for cheap on the used market.

the good news is, they have snapdragon models with super competent hardware and a good portion of them have lineageOS support (and by extension, many other derivative OS) - Poco F1 is one of the rare semi-modern phones that also has postmarketOS support.

the bad news is, the bootloader unlock process takes a week, just because; do yourself a favor and don't connect this monstrosity to your LAN while you wait for the timer to expire. also, they're chaotic (to say the least) with their model naming, with zero consistency what each suffix means (T, Pro, etc.) and it's not rare that they do a model "refresh" where they replace snapdragon with mediatek in the "updated" version.