Can I use a corkscrew on shabbos that is attached to my counter? I’m wondering if the Cork getting attached to the screw that is built in would be boneh?
This is fine. There is no problem in using the corkscrew.
This is not a case of boneh. The attachment of the cork is clearly unrelated to the counter (it doesn’t serve it in any way) and its attachment is entirely temporary, such that it doesn’t become part of the building. There is therefore no prohibition at all.