Hey there;
That was a “known issue” with Samsungs and LGs.
Important information about Plex for smart TVs after September 30, 2021 - Announcements - Plex Forum
I think this thread is specifically for only the laggy interface alone.
I should mention my Samsung got the update discussed by [sLumpy] some 28 days ago.
It’s better; but still not perfect.
