These are called M12 circular connectors. You could also use M16.
I would much rather find an RJ12 bulkhead connector, but I have had no luck so far.
Something to just mount an RJ12 socket into a wall, with a flylead to an RJ12 plug would be great. Or an RJ12 socket on both sides.
If anyone can help me finding one that doesn’t cost 25 euro, let me know.
Yes, something like that. But better would be one that only needs a round hole. Creating a nice square hole in your fridge wall can be hard. Also that page is a strange mix of RJ12 and RJ45.