I have this same issue with the Outlook add on, using Outlook Exchange server.
The Hubspot Sales login box opens blank.
The trouble shooting article doesn’t seem to cover this eventuality.
@Smiley1 do you open a browser first and sign in there? Instead of signing in through Outlook, I think if you sign in through a web brower to HubSpot.com that should sign you in for your email, giving you access to HubSpot tools. We do everything through Google workspace, but I’ve seen clients do the same with Outlook.
If not, have you contacted Support in your portal? I’d start there. It might be something they can walk through with you.