Trying to despawn mob after it spawns in once

Hello. I only started using Mcreator a few days ago, so this may be very simple

I'm trying to make my custom mob despawn after spawning once, then be allowed to spawn after it has despawned

Using a global variable, I tried to make it so that it could spawn only if it's "false", but it continues to spawn multiple over and over again. (Also, the mob spawns in completely transparent for some reason? It doesn't have a custom model, only Bipedal. Not as big as an issue as spam spawning.)

If there is another way to make a mob that spawns only once, please let me know

(using version 2024.1 and Forge 1.20.1)