ZDoom

Does Vanilla Heretic use the same map format as Doom, or is it its own format? I ask because I’m practicing with Doom Builder, & I would like to know what to set the map format to when making levels for Vanilla Heretic.

In terms of Doom Builder it uses its "own" format - which really is Doom format but it has its own distinct line specials and thing id's, few of which it shares with Doom. A map built in the Doom format for Heretic using Doom id's will be very broken. So it does need its own config.

If you're using Ultimate Doom Builder you can activate extra game configs in the preferences dialog as needed.

Technically the map format is the same as Doom; but yes you need to go enable the Heretic configuration in Doom Builder because of course it's a different game with different effects (different things, different line actions, different sector types, different textures and flats, etc.).

I’m guessing it’s the 1 labeled "Heretic: Heretic (Doom Format)" in the drop-down menu? I did check off all the configurations in case I miss anything. Also, I’m using GZDoom Builder.

Yes that will work perfectly fine.

Cool.