Disc brakes locked

Again..............you said releasing pressure at the caliper releases the brake. This indicates a pressure problem. If you bleed it at the caliper, it could be the hoses. If you crack the nut at the line at the master cylinder, and this ALSO releases the brake lock, then it cannot be the hoses---it must be pressure retained in the master.

Again............if the piston in the master piston is not returning, either due to wrong internal parts as in rebuild/ rebuilt, or wrong combo of master and pushrod / linkage, then that will hold pressure and lock them up.

I did this years ago on a 57 chev. Got the master together wrong, the master could not fully return the piston. Drove the car for several blocks, and in about 4 blocks, corners, stopping, etc, the brakes were dragging BAD

Down in your master there should be what is called a "compensating port." The piston MUST return fully to release this pressure.

Also pull up on your pedal and "feel" the linkage. You should have "some play" with the pedal all the way up