Hi all, just wanted to put this info here for other people with similar problem and maybe Avast developers if they read this forum. Avast and Lightroom (latest version) still dont go well together. I was analyzing the problem of extremely slow performance on my PC as soon as I start Lightroom for days. I am talking about up to 5 minutes waiting for just starting the Lightroom, watching how parts of its interface slowly appear on my screen. To switch to anything in the Lightroom or other desktop apps was making my PC unresponsible for up to 30 seconds.
Then I stumbled on an old article in this forum. Tried to uninstall Avast - and yes, this was the reason.
So, I hope this helps.