We usually buy veggies when in season and vacuum seal and freeze. Green cabbage is a favorite for Corned Beef & Cabbage so we freeze about 10 heads a year. Normally, we would cut in half, core and then quarter, vacuum seal and freeze.
The last time we just cut the head in half, sealed and froze. Anyhoo, just cooked a very nice Corned beef in the Instant Pot, removed it when done and then threw in 2 halves of cabbage brought the pressure back up for 5 minutes and it turned out perfectly and the core was soft and sweet and very tender. Never would have softened enough to eat in the crock pot.