I can sign into iCloud on my iPad but not my Mac!

I’ve got a 2009 Mac Mini running OSX 10.10.5 and a 6th Gen IPad running IOS 16. My iPad can connect to my iCloud account just fine, but my Desktop Mac won’t. I’ve tried everything for over a month now. I’ve changed my password numerous times, on both devices. My iPad connects every time, but my Desktop refuses to cooperate.

any help would be appreciated.