I believe jellyfin has an option to ‘burn in’ subtitles so they are part of the video. I don’t know how this effects performance or anything but it should work for what you described. I believe you can turn it on through the admin web ui.
I am not too knowledgeable on different encoders, but I don’t know if using cpu and gpu is an option. Av1 and vp9 are open standards, meaning basically anything can implement them, but av1 is new so older devices haven’t. The tv will probably handle vp9 fine, but I would still recommend transcoding a test video and looking if it plays back natively. With that gpu av1 is definitely not supported so I would recommend vp9.
First, just to be clear because codec terminology can be weird, x264 is a h264 encoder, not a separate codec. H265 is not an open standard so it may not play back properly if you use a Firefox or a Firefox based browser. I would recommend av1 if you can encode it, as it is good for quality and file size, however only new GPUs can encode it. CPUs can encode it slowly, but if you don’t have a new gpu (like 40 series Nvidia, arc, or AMD 7000 and maybe 6000) I would recommend vp9. It is a bit worse for file size but it won’t take a year to encode and should be compatible with most browsers.
I only watch Rossmann’s channel anymore so I will probably just quit if they block mine. I use uBlock Origin + Librewolf + VPN + pihole + a random user agent extension. When I set my VPN to USA it still doesn’t say anything.