There won't be a FOSS alternative for TVs. TVs have regulations that come with them in many countries. There is no way to make a FOSS "TV" that respects you as a customer.
We however can buy Large Format commercial Displays. They will cost more, but that's the solution.
There are lots of closed devices that smart people have found exploits for that they use to install open OSs and firmware. If companies are going to be this combative, seems like an obvious place for a counter strike. If right to repair can gain more momentum, the movement absolutely needs to include being able to install your own OS on any device you own.
From what I understand, TVs are incredibly customized and locked down by design. Not only that, they change very often and by the time you make a cracked firmware, the TV is no longer in production.
Is it possible, yes. Is it worth your time? Probably not but hey I would love to see it be done! Imagine TCL seeing a sudden uptick in TV sales because someone found out how to remove the Roku from the Roku TV.