Used to live in Strasbourg, so regularly did multiple FR/DE/CH crossings in one day - particularly when cycling along the Rhine.

Probably the most in one day was when heavily delayed at BSL airport (which has a French zone and a Swiss zone) where there were multiple problems, resulting in some facilities only being able on one side, and some only on the other!

I have driven overnight UK-FR-BE-LU-DE-FR. I don't recommend it. FR-IT-FR-MC-FR was much more fun

With train journeys, disappointingly few multi-border ones. Lots of single-border ones, but otherwise UK-FR-BE (lots of people do this one), AT-CZ-DE, PL-SK-HU, HU-SK-AT-CZ, AT-LI-CH-IT.

By bus, even less. HR-BA-HR-BA is probably the biggest (thanks to the Neum corridor).