Dear Marcos M_365,
Good day!
Thank you for posting to Microsoft Community. We are glad to assist!
Based on your description regarding "Can't add account to Outlook desktop app". Kindly check with below methods to see if it will make any difference:
Note: Before performing this, kindly close all office Apps.
++ Kindly try to disconnect account from Work access or School:
Click On Windows Start Menu
Settings
Accounts
Work Access or School
Select the account and click on Disconnect
++ Kindly try to clear credentials
Open Control Panel > Credential Manager.
Select Windows Credentials
Remove all Windows credentials listed for Office16 by selecting the drop-down arrow and Remove. (remove credentials related to the account you want to add)
++ kindly try to remove the account from Registry key
On your keyboard press Windows Key +R(Or Click on Windows Start Menu and Search Run)
Type Regedit
Navigate to this path :HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\Identity
Expand Identities folder
Select on each folder and check which folder shows the email address of the account you want to add
After locating the folder, please right click on it and delete
++Kindly try to Create an Outlook profile - Microsoft Support please do not delete old profile to prevent the loss of your data.
If the issue persists, would you mind offering below information:
May I please know if this issue occurs to Outlook only or all Office apps?
May I please know if this issue occurs in both New Outlook and Classic Outlook?
May I know your current environment? Is It Exchange Hybrid, on-premises exchange (Exchange server) or pure cloud?
Would you mind to kindly provide the screenshot of the outlook version are you using?What version of Outlook do I have? - Microsoft Support
Looking forward to your response.
Best regards,
Inema |Community Moderator