Go to team settings in Microsoft 365 admin center > admin >Teams >Manage teams.
Select the team you reside and click edit to check whether the team support adding, editing and remove apps.
3. go to Teams apps>Set up policies to check whether your team owner allow “Upload custom apps” and set it to 'ON'
4. 365 can take up from 30 minutes to 1 hour for this setting to apply. So wait and check back and walk through the steps again after this has been turned back on.