iOS 14.5.1 introduced these problems for me. Spent a long time troubleshooting failed iCloud backup for 14 days. No photos sync, no backup, no warnings. After a complete factory reset, the apps did not download automatically. Clicking on one app, the OS asked me if I wanted to wait to download on Wifi bue to size... but the phone is on wifi and surfing the web fine...
Checking mobile data logs, it's clear that although connected to wifi, the phone is downloading over 4G network.
iCloud still refuses to backup.
Same for all phones and iPads in the household with Asus router.
How come this is not fixed after such a long time?