Well, this is how it went.
I had a brief window to play with the television. I don’t know if this helped in any way whatsoever but I enabled developer options by clicking the build number in Android settings five times (maybe more but the interface shows a countdown so you know). However, I’m 99.99% convinced that this did not make any difference to the eventual outcome.
The Philips TV Home Screen/launcher is an ad-fest full of garbage that does not interest me and there is a row of apps along the middle which you can add to but when you try to add apps, you can only see apps which the TV shows in its curated installed app list - so if it isn’t listed, you can’t add it to the launcher, neither can you change the launcher (I have an Android TV box so I can see how the settings usually are). However, you can install a launcher, which I did, and when the launcher is opened, all the apps which seemed to disappear after being installed are listed, including Brave and Opera.
Unfortunately, when Brave was opened, the screen went white, then rotated 90°, went black then quit. Opera would work so using that, I found and installed the Bravearm64Universal.apk mentioned earlier. When I launched that version, I got the rotating white screen again, then black then a Brave splash screen at 90° but then it quit - but some kind of progress.
I then tried installing BraveMonoarm64.apk. That also did the rotating white screen, black screen, 90° Brave splash screen but went to a 90° welcome screen with options which were almost impossible to navigate at 90° with an air mouse but I managed and thankfully, the screen rotated 90° back and seems to be working.
I don’t use the television for watching anything other than SmartTube, Rumble and Kodi, so all the stuff that it tries to ram down my throat is wasted and it is a pain having to find stuff it hides from me. I’d be happy with a Home Screen with nothing but a few buttons to the apps I use- but it has a great picture and it was at a fantastic discount about three years ago (though I bought it new it was a two year old model).
Anyway, all seems to be good(ish) now. Thanks for the contributions.