Help, please! iCloud issue; files not syncing WhatsApp not backing up

I been using iCloud for 15+ years, my recurrent equipments are an iMac and a MacBook Pro, in some different versions. Late last year I started using a PC and I downloaded the iCloud app in order to use iCloud there as well.

At least a month ago I realized that some of my files were not syncing, they remained marked with the dotted cloud. Files created in the PC were not appearing in my iMac or MacBook.

I also noticed that every new file I made on my iMac or MacBook were not syncing; and also my WhatsApp chat backup is not syncing either (I use an iPhone 16 pro max).

I signed out from the PC thinking that could be the problem, but the problem persisted.

I tried to access iCloud.com via web page, I placed my user and ID and allegedly I gained access to it but it didn't load completely when I was sent back to the sign in page. I even get the emails that I have accessed to iCloud.com

This has been happening at least for a week. None of the troubleshooting that I have found is helping me.

I really need help with this issue, please.

Thanks