I can give them the sword or the crossbow to turn them into guards them but nothing else. i cannot open their inventory. i tried in creative mode, i had "hero of the village" as well but nothing, no inventory. I play this mod on 1.16 from the modpack "Better Minecraft"

We don't support 1.16 anymore and you can only get into the guards inventory with hero of the village in that version, not also by converting a villager into a guard.