When I need an avatar, I use boringavatars.com -- but instead of using the site, I use this url with a generator I made in Google Sheets.

The trouble is, it spits out an SVG. To quickly save it, right click on the SVG > Inspect > right click <rect width=... and select 'capture node screenshot'

There are extensions that do this or something similar, but unless you're exporting SVGs in bulk, they're largely unnecessary.