This is a flat, substabtial interface with the 10th Amendment’s allowance of states to manage and run elections. If a state allows elections such that they aren’t denied on account of race, gender, and people under 18, they can be run however the states deem. Requiring someone to register with the federal government is not a power of Congress
Pretty hard to drop your ballot off at a drop box when you never got it because the postal service disappeared it.