This sounds frustrating, especially since it was working fine before. A few things you might want to check:
Microsoft 365 Personal Limitations: The Personal plan doesn’t support full Teams business features like external scheduling or managing Teams orgs. If you were previously using a workaround or a free Teams version, recent updates may have restricted that.
Try Using Outlook Web: Sometimes scheduling via Outlook on the web allows more flexibility than the Teams app itself—try creating the meeting there and inviting participants.
Clear Cache or Reinstall Teams: If it’s a glitch, clearing the Teams cache or reinstalling the app may fix it.
Check if You’re Logged into the Right Account: Teams can get confused if you’re switching between personal and work/school accounts. Make sure you're using the same Microsoft account throughout.