The UK has already done it.

"The UK has suspended the operating permit for Belarusian state airline Belavia, and EU leaders have called on member states to take similar action."

https://www.bbc.com/news/world-europe-57236489

Given that Minsk to London Gatwick is Belavia's furthest west flight (B2851, three times per week), this has limited effect.

Belavia has no reason to fly over UK airspace otherwise.

Switzerland is interesting. There's no way for a plane to get to it without crossing EU airspace.. I wonder how that plays out.

In the interests of pedantry, there are several ways. The simplest might by to bring the plane over land. There's also the option of going above the vertical limit of the controlled airspace, which seems to be debated, although it must be at least 30km, and less than the boundary with "space" which must be near the Kármán line at around 100km. A tunnel would be possible also, but prohibitively expensive. It would probably be cheaper and easier to get Hungary and Austria to leave the EU.

Barge up the Rhine