Do i need a covid certificate to go and shop in Germany from Switzerland. I'm just wondering now since the covid situation is on the rise again.

Nope, nothing other than you have to use a disposable, medical-grade mask (you'll be turned away with anything else). It's a mirror of pre-pandemic (except for Mehrwertsteuer). They stop the occasional person to check what they've bought, but there's nothing beyond that happening. You can freely come and go with ease, as things currently stand.

At the moment, France and Germany are open to cross border shoppers. That can change. Just before Christmas, Germany decided to not allow Swiss residents to come and shop. We didn't know until the lady at the checkout told us... but we made it back with our goods (no MWST refund though) without being arrested!