well anything based on android TV can be easily modified with sideloaded APKs for excellent compatibility and upgradeability, there are also some package sideloading techniques for LG and Samsung but they are less open and there is less to do when you do jailbreak them. the issue with this, even on the top of the line TVs is that the hardware eventually gets out of date, and format/codec support is locked to that hardware so an external device is always a better option.
Buy the TV with the image quality you need and want in your price bracket (don’t look past TCL and Hisense these days), then plug in any of the top external streaming device and just leave the TV offline other than to check for firmware updates occasionally.
The Nvidia Shield pro 2019 is getting old but it is still the king for home media servers using plex or jellyfin, only weakness is no youtube HDR but thats not a big loss. great support for dedicated theatre setups with Dolby Vision, Atmos, DTSX etc…
Chromecast google tv is actually pretty good for most people for “normal” use with the standard streaming services and is pretty good at plex or jellyfin if you get an ethernet adaptor for it. DV and Atmos support is there but isnt perfect.
Current gen AppleTV is pretty good for all general playback, but is less hackable, so app support is limited to whatever is in the store, jailbreaks might be possible in the future as usual with apple devices, but I havent researched them.
the cheaper android boxes like the xiaomis and the microbrands on amazon all vary in quality and some are downright dangerous, but if you know android you can probably clean them up by stripping out crap with ADB commands.