The 183 day rule in the Schengen Zone?!

Does anyone understand how the 183 day rule is enforced in the Schengen Zone? Hear me out, the border between Portugal, Spain, and France essentially never has any passport control.

If I was an EU citizen but paid tax in the UK, stayed in either country for longer the 183 days in a year, how would I even flag up the local government's radar? Say I have a connection who owns/rents their spot. I live with them and work online from their spot indefinitely, unless some very improbable event (theft, injury etc.) occurred I would presumptuously never appear on any radar?

I just find it intriguing. Does anyone know more about this?