Today I finally managed to take out the problematic oil pressure switch. This combination of tools did the trick. The crowfoot spanner was essential but it still wasn’t easy to find a suitable combination. Today I finally found a tool store that was selling those.
But then there are the bad news. The switch works. I tested it with a bicycle tire pump. So that means that my oil pump is likely the culprit.
Before opening the engine I’m going to add a pressure sensor to the oil filter housing and crank the engine (with the ECU fuse removed) and see what happens.