@Joelewes
It might be worth repeating your query in the ‘Other’ section here, see if you get more Linux TV owners or experts looking at the issue.
Meanwhile, here is yet another Sony article on this, which is at least from a 2020 date:-
https://www.sony.com/electronics/support/articles/00145689
The only other thing is could you post a screen shot or screenshots of what you see when trying to do this, so we aren’t flying blind trying to find the same dialogue on Google?
My favourite bedtime reading is a Sony product manual…
