Better alternative: Teams personal tab

Supported platforms: Teams desktop, mobile, Teams web, Microsoft 365 web, Microsoft 365 desktop, Microsoft 365 mobile, Outlook desktop, Outlook web, Outlook mobile

No support for Mailbox and Item events, which means no new window email ecetera

Documentation

Extend a Teams personal tab across Microsoft 365 Teams JavaScript client library Publish Teams apps for Microsoft 365

Samples

https://github.com/OfficeDev/m365-extensibility-image-editor?tab=readme-ov-file

Editable todo list with SSO built with React and Azure Functions. Works in Teams, Outlook, Microsoft 365 app.