No, guests do not need to have Microsoft Teams installed to join a meeting.

When you send a Teams meeting invite, participants can join using any of the following options:

• Via Web Browser - Participants can select the meeting link and select Continue on this browser to join without installing the app.
• Via the Desktop or Mobile App - If they do have Teams installed, the link will open in the app automatically.
• By Phone - If the meeting includes a dial-in option, invitees can join by calling the provided phone number.