Catalina Photo Issues & upgrading to Big Sur

I have my entire Photo Library on an external drive which under Mojave was all running fine. As soon as I upgraded to Catalina it all went haywire - extremely slow to load the App and also very slow to load pictures. It is quite plainly not fit for purpose.

From a bit of research, it is clear that I wasn't the only one having photo issues on upgrading to Catalina. I now see that Big Sur has been released without, as far as I am aware, the existing issues with Photos in Catalina being resolved.

My question is this - has anybody here upgraded to Big Sur who initially had the same problems I had with Catalina? Has Big Sur sorted out this mess that Apple have done nothing about? I honestly wish I had stuck with Mojave as Catalina has been a bit of a disaster - certainly where Photos is concerned.

Grateful for any insight - thanks.