Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
Greetings!
This is Tin, sorry to hear that you cannot save on your MS Excel while having MS Office 365 subscription. May I know what is the error message that you're getting?
Please try to check the status of your subscription here: https://account.microsoft.com/services
If it's active, please try to sign out your account on MS Excel app and sign back in.
To do that, please click File Tab, click Accounts, then sign out your account.
Relaunch the MS Excel app and sign back in.
Please check if you're getting the same issue.
Let me know how it goes.
Thanks,
Tin