Works perfectly fine for us supporting our traveling sales personnel. No VPN needed afaik.

Not FOSS, but if you’re working an in windows environment: Windows Remote support. Easily started by pressing 3 buttons (Ctrl+Win+Q) and ships with current Windows versions.

You’ll have to set some settings via GPO to be able to do admin stuff with elevated rights but it served us well since we ditched TeamViewer half a year ago.