Sending, receiving, and organizing email in Outlook.com
What happens when you try to delete the rule?
What is the name of the folder? What happens when you try to delete it?
Did you change your password and if at all possible, enable 2-step verification, with at least 3 forms of verification?
And also sign the account out everywhere and reset windows hello at the bottom of https://account.live.com/proofs/manage/additional
You should also create a recovery code at the bottom of that page, especially if you enabled 2-step verification. Keep the code in a safe place and don't forget where it is.
Do you have a subscription for Microsoft 365 software? If yes, add the account to classic Outlook and after it syncs, close Outlook and reopen it using the /cleanrules switch. To do this, press Windows key + R to open the Run dialog. type or paste the following into the Open field and press Enter or click OK to restart Outlook. (There is a space before /)
outlook.exe /cleanrules
Note: if classic Outlook is not installed, you can install it from here: https://support.microsoft.com/en-us/office/install-or-reinstall-classic-outlook-on-a-windows-pc-5c94902b-31a5-4274-abb0-b07f4661edf5
-- Diane