One idea - if you are using distance maps in your scene, maybe they are being updated in the background by Slate. Make sure to *not* display scene materials in the Slate browser, maybe this helps.
There are performance issues with Windows UI scaling, too. If you are using it, see if changing it to 100% helps.
In general though, Slate is going crazy with the internal notification system and that's what is making it slow in general.
Slate's material/map browser is really slow here. I can't use Slate on our heavy assets, literally *any* change to a material which involves the Slate browser - assigning or changing maps or materials - takes minutes.
Autodesk is aware of this since quite a few years, pages of reports and discussion have been going on for a really long time. There were some attempts to improve this in 2021 and 2021.3... but still, the old material browser is much much faster.
One Autodesk dev suggested to :
-close Max
-open 'SME.ini 'located in 'C:\Users\YOUR_USERNAME\AppData\Local\Autodesk\3dsMax\2020 - 64bit\ENU\plugcfg_ln'
-change the line 'LibSceneMtlOptionFlags' from its current value to '0'
and see if it helps... in my case it made no difference whatsoever.
Like I said, the problem is not going away probably unless SME 2.0 is there. How long will this take... years, probably.
BTW, you can still use the old material browser, maybe this helps. Try it out by changing 'UseOldMtlBrowser' to '1' in the same ini file.
If you want to see a change, report it as a bug, make sure to post on the Area etc. Most rendering devs have not much experience in using Max in a production environment, or are long gone from any production role, and simply have no idea how much it slows down people and make working impossible for some.