I have 5g of storage available I am using 3.5g. I get an error that there is not enough room in icloud to back up.WTF?

Unless you hardly use your iPhone storage for anything, 5GB for an iPhone 11 isn't much. I do manage to have 4 devices backed up to my 5GB iCloud but I only have 15 photos on my devices and maybe a dozen non-Apple apps. I suspect that is very unusual compared to many users.

How to check the storage on your iPhone, iPad, and iPod touch - https://support.apple.com/HT201656

Click on this link to read how to 'Manage your iCloud storage' --> https://support.apple.com/HT204247 - including seeing how much storage you have and how to delete items stored in iCloud such as backups, photos, files, mail, messages and voice memos.