a millstone around (one's) neck

An extremely difficult or disadvantageous burden or hindrance. I wish I hadn't bought that house—the mortgage is a millstone around my neck. Given the advisor's laundry list of scandals, he's proving to be quite a millstone around the candidate's neck. Supply-chain problems can be a real millstone around your neck when you work in the manufacturing sector.

a millstone round (one's) neck

An extremely difficult or disadvantageous burden or hindrance. I wish I hadn't bought that house—the mortgage has been nothing but a millstone round my neck. Given the man's laundry list of scandals, he's proving to be quite a millstone round the candidate's neck. Supply-chain problems can be a real millstone round your neck when you work in the manufacturing sector.

a millstone round your neck

a very severe impediment or disadvantage.

A millstone was a large circular stone used to grind corn. The phrase alludes to a method of executing people by throwing them into deep water with a heavy stone attached to them, a fate believed to have been suffered by several early Christian martyrs.