go to gsmarena and filter phones by chipset. select something like Snapdragon 845, a widely supported SoC that is at the cross-section of hella old i.e. cheap but also super capable; it’s doubtful you’ll ever need anything faster than that. then see which of the filtered models you can get for cheap. finally go over to lineageOS and see if it’s got current support.
that’s a hella rad machine to convert because of something so easily fixable. could be due to a loose cable, or needs a new panel; provided it ain’t of the ultra-spensive variety, 2nd hand laptop panels can be had for like $20-50 from your local junker. short of that, converting it to a full desktop would be the next best use case. using a hexacore ryzen with 3050ti as “media PC” is fucking bonkers, a potato can handle that.
littlefedi is out as of coupla days ago. still in early stage but should cover your use case. local binary, world comms via “lighthouses” don’t need domain, vps, etc.