I have this issue as well on multiple Tahoe Macs. Opening a new Safari window is 500ms to 1000ms. Adding a tab is faster most of the times. But Safari frequently loses tabs turning them into a blank page without a URL. Searching in the passwords app talkes multiple seconds. This is on multiple macs with different icloud accounts even.
I don't have that problem (new Safari window in < 100ms) but I believe you, LOL.
Because I have the problem on 7+ Macs (as in all mine, my kids', my sister's and my dad's (all of which I am primary tech support on)) where if I press ⌘+ to increase the font size on a website, it increases — and then immediately reverts back to the previous size.
Every single time. But only the first time. I just did it on this site to be sure it still happens.
Do it again, and it works.
It's been happening for at least one or two years, across more than one major OS upgrade. ¯\_(ಠ_ಠ)_/¯
