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Google Meet allows the meeting host to share multiple screens simultaneously or to allow the host and a participant to share screens at the same time. Here's how:
Sharing Multiple Screens in Google Meet
To share one or more monitors while in a Google Meet, follow the instructions below.
1. Within a Meet, click the Share Screen Icon in the menu at the bottom of the screen.

2. Choose what tab, window, or screen you wish to present and click Share.

3. In some situations, upon screen sharing, your shared screen may show up as a small picture in a picture window, rather than in the main Meet window.

To bring your shared screen back into the Main window click "Bring the call back here" or click the the "Back to Tab" icon in the top right of the pop-up window.

3. A SECOND PERSON can then click Share Screen, choose the tab, window, or screen and click Share.
Alternatively, the
4. HOST can share a second screen by "re-joining" the Google Meet. This can be done by clicking on the invite link in their Google Calendar.

5. Then, rather than clicking "Join Now," host should choose "Use Companion Mode" and then follow the share screen instructions above.

Shared Windows appear small. Here's how you can adjust:
When multiple screens are being shared, HOST should pin the relevant screens, so viewing is easier. (For best viewing, don't pin more than two screens at a time.)
1. Hover over the important screens and click the Pin Icon > for Everyone.

With two pinned screens, the host and viewers should see something like the below, which involves two larger shared screens and smaller individual thumbnails of participants.

Additionally, individuals have two more options available for improving the viewability of the shared screens.
2. Participants can hover over either shared screen and click either Zoom In or Full Screen to enlarge it.

3. All users can also re-visit their three-dot skinny snowman menu and choose adjust view, to change the overall layout of their screens. (Spotlight view works well when dealing with pinned screens.) The slider below the layout types allows users to make the windows larger or smaller as well.

Additional Resources.
Present during a Google Meet meeting:
https://support.google.com/meet/answer/9308856
Pin or mute Google Meet participants:
https://support.google.com/meet/answer/7501121
Change your layout in Google Meet:
https://support.google.com/meet/answer/9292748