P: Slow UI when using Mac and Custom Display Profile

It's not just slow. The masking has issues. Check it out. Would recommend reverting to V9 for now.

Thanks! 
I'm back on V9.4 What a difference!

By the way, I tried your tip regarding SSD. It did not bring any improvement for me. A library with 1200 photos is not manageable in V10.

This is really embarrassing! 

When upgrading the catalog LR automatically creates a backup of the "old" catalog. As the upgraded one is not compatible with older versions, you need to find that last backup and open it with the previous version (that you need to reinstall of course, in case you already deleted it)

Give it a try, it’s what made the difference for me. I had tried all of the above before as well with no success.
Seems to me the new version is making a lot more requests to the RAW files than earlier versions

How can I go back to the old version? V10 is not usable!!!!!

I noticed this too. Develop module was more usable but still noticeably slower than 9.4.

I tried all that as well, except for moving the images to my SSD (Samsung 970). I'll have to give it a try.

Maybe a useful additional information:
The thumbnails in the Develop module (bottom row) are very fluid!
But the library module is terrible (not usable).

Same for me!

Inredible Slow scrolling! 

macOS Catalina

Modellname: Mac Pro

Modell-Identifizierung: MacPro6,1

Prozessortyp: Quad-Core Intel Xeon E5

Prozessorgeschwindigkeit: 3,7 GHz

Anzahl der Prozessoren: 1

Gesamtanzahl der Kerne: 4

L2-Cache (pro Kern): 256 KB

L3-Cache: 10 MB

Hyper-Threading Technologie: Aktiviert

Speicher: 64 GB

do we really need to have flame wars here, too?