Hi Laurencheill,
I'm Nik, an independent advisor here to assist you with this.
Yes, yes can join multiple Organization team as a guest.
Please follow the steps to join a team as a guest from here:
https://support.microsoft.com/en-us/office/join...
Also, once you join one Organization it allow you to switch between Organization.
If you already use the Teams app in your organization joining a team as a guest is a lot simpler.
- Just open Microsoft Teams app and choose Yes to switch to the team you are invited to. Now you can collaborate on the project in Teams.
- To switch back to your company's team, select it from the Organization drop-down.
Regards
Nik