A Microsoft file hosting and synchronization service.
Hello Vladan Ljubisavljevic
Being signed in to Microsoft 365 does not necessarily mean that the OneDrive sync app is connected to the same account.
Select Start, search for OneDrive, and open the app. Sign in using the same personal or work/school account associated with your Microsoft 365 subscription.
If the account is already listed, select the OneDrive cloud icon near the clock, then Help & Settings > Settings > Account > Unlink this PC. Reopen OneDrive and sign in again. This will not delete files stored online.
You can also sign in at Microsoft365.com, then select Apps > OneDrive to check whether your files are accessible online.
If the problem continues, please provide the exact error message or error code displayed during sign-in.
I hope this helps.
Feel free reply back to this post if you need further assistance, I'll be happy to help.