The Artemis 1 mission is going to do a wet dress rehearsal where the rocket will be filled with propellant and the launch sequence will continue until almost the last second. The launch sequence will then end. What happens to the propellant? Is it a universal procedure for all rockets? If not, what happens to their propellant?
A reputable blog, Spaceflight Now, says that
...culminating in a hold at T-minus 9.34 seconds, just prior to ignition of the main engines.
Then the core stage and upper stage will be drained of cryogenic propellants, and NASA engineers will evaluate the rocket’s performance during the dress rehearsal, before eventually rolling the rocket back to the Vehicle Assembly Building.
NASA agrees that the wet dress rehearsal includes
...practice the launch countdown and then recycle [sic: rewind?] back to T-10 minutes to demonstrate the ability to scrub a launch and de-tank.
Organic Marble's answer, that detanking returned as much propellant as possible to off-vehicle storage tanks, applies to large rockets more recent than the Space Shuttle if for no other reason than ground crew safety, as that answer's source says. Indiscriminately dumping onto the ground that much LOX or LH2, or both, is asking for all kinds of trouble.