Under the Constitution, state’s have sole responsibility for the selection of Electors. The only Federal issues would be if voting rights are being denied based on a poll tax, gender, race or ethnicity or age (for those over 18). States also wouldn’t be allowed to make the position hereditary (under the “republican” form of government clause. Indeed, a state theoretically could have the legislature elect the “electors”.
Trump created a strong “originalist” bias in the Supreme Court, which will serve to limit both him, Biden and subsequent presidents. This may end being the best thing Trump will be remembered for, though he wouldn’t think so (he really wanted “red meat” conservatives, but someone was talked into “originalists” instead).