iMac performance degraded, longer power ups after upgrade to Sonoma

I installed Sonoma 14.0 the day it came out. I installed Sonoma 14.1 the day it came out. It's been a couple weeks since then, and I'm still seeing several issues I never saw before Sonoma:

1) My Mac takes much more time to power up.

2) General performance is slower than it had been, sometimes so annoyingly slow that I restart hoping it'll help.

3) Three times so far, on power up or restart, my wallpaper has reverted to a forest scene rather than the personal photograph I'd set.

4) I get pop-up reminders for tasks I'd marked completed the day before.

The computer is a Retina 4K from 2019, and I wouldn't expect it to be getting old already.

I tend to shut it down at night and turn it on in the morning, so it ought to be running "fresh," whatever that means. (I got into the nighttime-shutdown habit years ago with Windows and UNIX devices that seemed to work better that way.) While running 14.0, I got help from tech support to clear cache, and that helped performance for a little while. I've run Malwarebytes a few times, and it hasn't reported any issues.

Is anyone else seeing or reporting these issues?

[Re-Titled by Moderator]