I’m totally frustrated by this - my iPhone has now ‘not been backed up for 24 weeks’ it shouts to tell me every 5 mins - I have done manual backups but because I don’t use the latest OS on my Mac mini and my home WiFi is a shared network between residents, I cannot log in to sync as such - it just begins to tell me that it will take 2 mins, 500 mins, 35 years lol! I can’t get it done in Macdonalds either as someone above says - as a result I have hundreds of duplicates photos and videos and a permanent petulant ‘this phone Has not been backed up.. blah blah blah’ every time I use it - I’m so tired of it - I’ve used Mac’s for over 25 years and this is just **** - my 50gb of cloud storage is almost used up with the continual duplication - some 400 photos and 30 videos now mushroomed to take up 15gb alone - I know!!! And all because I can’t afford a new Mac and live in a new build with shared WiFi - F F S in very big letters loool - new iPhone, loads of space, latest IOS etc etc - sucks teeth - even went into apple store and they didn’t want to help ....
Sounds like all you need is a proper network connection to the cloud. Are McD and your home the only useable WiFi networks for you?