Although it is vulnerable to a vorpal sword, ironically, as a creature with legendary actions, it is immune to the Vorpal Sword's decapitation ability.
I think this is the sort of enemy that you have to stage the appearances of carefully to actually have be interesting or compelling. The Confusing Burble looks pretty devastating to most groups that aren't prepared for it. A 30 foot aura of DC 18 Charisma save each turn to be able to control your character is pretty rough for any melee combatants who aren't Paladins with double Charisma bonuses to the save (even a melee Warlock or Bard with high Charisma and proficiency in the save is probably going to fail that half the time without buffs). But if they are prepared for it it can be completely nullified by anything that eliminates sound, leaving the Jabberwock as basically just a mid-level dragon. So if they have their one and only fight with it knowing what they are in for it is likely to not really display the power of this monster.
I'd probably go with having their first encounter be interrupting it terrorizing a village or something, with no warning about its abilities, have it stick around for a round or two before just leaving, carrying off a villager, cow, etc. for its lunch. Then they can research it, track down a scroll of silence or special ear-sealing materials, possibly quest for a vorpal sword, and then go slay the jabberwock.
I'd also probably change the regeneration to being stopped only by a vorpal weapon rather than general slashing damage, if such a weapon was appropriate to the campaign. Quest to find the macguffin that can stop the otherwise unstoppable enemy is the sort of straightforward, clear-goals, tropey thing I like for an overarching campaign plot.
