Google as of May 1, 2025 has turned off POP/IMAP access to Gmail from Outlook app because Classic Outlook app is "less secure". This can be fixed.
Basically, you need to set up 2-Step Verification on your Google account (no this is not phone verification). Then go to "App Password" at the bottom of the 2SV page. Enter "Outlook" and get a new 16 character password, and replace your Outlook login password to your Google account with this new password.
Note: On Outlook, you may have to remove your account to connect to gmail, and then create a new account with the new password.
I posted this yesterday. For more details, checkout:
https://answers.microsoft.com/en-us/outlook_com/forum/outlk_win-outtop_classic-outsub_ofh/how-to-repair-classic-outlook-to-access-popimap/6090863f-0991-41ed-9544-130b43122156
Are you using Classic Outlook app connected to Gmail via POP or IMAP?