Hi Paul,
Please go to Settings > Accounts > Email & accounts > Accounts.
Select the account that you're using on your apps and please make sure that it is set to 'Microsoft apps can sign me in'. If it is already set, try to remove the email then restart your computer.
If the issue persists, we can try the troubleshooting listed in the below mentioned thread.
Microsoft 365 desktop applications keeps logging out of account - Microsoft Community
Please update with your findings!
Sincerely,
CK