I.G. you could have changed the psw switching to 2FA. So, in Linux, Dolphin o any other file manager could not recognize any more your cloud webdav.
To fix this problem, try the following steps:
1. in system settings -> KDE Wallet -> Wallet Manager -> Passwords – > Maps,
2. find your old cloud account and delete it,
3. then you will asked, as expected, for a new user and password.
4. And then it should work.