The 1.16.5 Hotfix version wont allow me to set a NPC invunerablity to false. Am i missing something? Ive tried the Npc edit command
Thanks!

Have you tried the following commands?
/data modify entity @e[type=taterzens:npc,limit=1,sort=nearest] Invulnerable set value 0
/data merge entity @e[type=taterzens:npc,limit=1,sort=nearest] {Invulnerable:0b}

Additionally, have you tried checking the Taterzen's data with the following commands?
/data get entity @e[type=taterzens:npc,limit=1,sort=nearest], then look at the Invulnerable tag's value.
/data get entity @e[type=taterzens:npc,limit=1,sort=nearest] Invulnerable

Yes, Thank you it worked!!! Also, Just a suggestion, mabye make it so that you can change if NPCs can sprint and also if hostile mobs can attack that NPC.
THANKS THOUGH!!!

Also the abilitys for NPC's to heal would be nice

also if hostile mobs can attack that NPC.

Mobs won't attack invulnerable entities, that's why suggestion pops up (to disable invulnerability) when changing behaviour to hostile.