It's a good idea, but I think the core problem here is that there's nothing to create such a tag from. And that's not something Roll20 could fix. In D&D 2024, humanoid is the category used for humans, elves, and other non-monsters. Goblins and Hobgoblins are now Fey, and Kobolds are now Dragons. This is a change from the 2014 book. So if you search humanoids in the 2024 compendium what you should get are only things like Guard, Wizard, Noble, etc (I can't test as I only have 2014 content). If you play pure 2024 and don't include 2014 content, you could at least use a humanoid search that way. And 2014 wasn't really any better. The MM gave NPCs their own chapter, but the statblocks are alll just marked as Humanoid, with the added complication that there were humanoid monsters (Goblins etc) elsewhere in the book. There's nothing to distinguish a Guard from a Goblin other than the name (well, they did use subtypes, like (goblinoid or orc, but there's no "human" subtype, so that guard at the gate could be an orc). Looking at adventures doesn't seem any different. My hardcopy of Ghosts of Saltmarsh has a chapter titled Monsters and NPCs, but the NPCs are only marked as generic humanoids, like Pirate Captain. The actual named NPCs in that book are described in text, which treats them like PCs with personality traits, but references humanoid statblocks like Gladiator. But there's no statblock for the named NPC themselves and there doesn't appear to be a compendium entry for any of them. Wizards hasn't provided anything to base an NPC tag on. Third-party content could do that for their NPCs, but it would probably be easier to create an NPC category in any compendium they provided, parallel to Monsters, rather than a tag within it (presuming that's feasible; I know nothing of content creation).