Can my non-resident bf drive my car in Switzerland?

Had no idea this was a rule and I've been repairing my car over the border for years and driving German loaner cars back and forth.

Always learn something when I visit EF!

So can I as a UK resident now fly to Geneva, use my SIL's car -GE plates and drive to Dijon to visit relatives. Or is it easier to just hire a Swiss plated car at the airport, use in in Switzerland but can go over to France?

Sorry to ask but had conflicting answers..