Unfortunately the preinstalled old clients suck and there is no way for Plex to update them (this is on the TV manufacturers). If you are otherwise happy with your TV, you can get a better client via a HTPC or streaming box (such as nvidia shield or apple tv). Jellyfin clients might work better on those as well, e.g. you would get less transcoding.

Out of curiosity, which Plex client are you using?