Why am I receiving iCloud login prompts on my HP laptop?

Whenever I boot my HP laptop, I get a popup window that sez "login to icloud for windows". This is a fairly recent occurence, so I wonder if it has something to do with various software updates, but I can't point to any particular one.

I never had this problem until this last year... I installed icloud for windows on my Zbook when I got my first 'pad in '15 and never had to log in again. I bought a new mini-6 ipad last summer and signed up for icloud+ to have the storage for photos, etc. Now, every time I boot the laptop, I get a popup telling me to login to icloud. I try, and get a security code on my iphone 12 mini, which I dutifully put in the app. and it flashes a new window that say's "continue to login to icloud". The popup is big enough it obscures most of the screen, but otherwise seems to be a normally functioning window. I can move, shrink, or kill it, but it won't stay away and blocks everything else on the screen. I've tried changing passwords, cold booting, changing usernames, and killing it in task manager. the last seems to make it stay dead. I can access icloud thru my Firefox browser, and it works normally. its just when I try to look at icloud photos with the app that I have trouble.

[Re-Titled by Moderator]