The shop you brought it to should be held responsible. It sounds like they may have damaged the logic board; VFD001 in Apple Diagnostics indicates that the internal display is not being recognized. They should return the Mac to you in at least the same condition that you brought it in to them as.[br]
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I think the 23" display thing is because of Anydesk, and perhaps it is interferring with displaying an image to an external monitor.[br]
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Maybe if you can find a store that does free diagnostics they can tell you what really happened.