You can replace your background with an image in Google Meet, using the default images supplied, or by uploading your own image.
To change your background in a meeting:
Click on the ellipses along the bottom of the screen
Choose Apply visual effects
The effects pane will display.
Click on the second button to add a small amount of blur to your background
Click on the third button to add a larger amount of blur to your background
Click on a background to use that image - animated images will show a play icon over them
Click on the + button to add your own image from your computer - locate the image you wish to use, then click on Open
Click on the first button to reset your background.