Preventing minecraft from generating nether portal and end exit portal at a specific y level

Hello! I making a void world (like skyblock not same) where the 3 world are empty and have a barrier floor at a certain y level (y -100 overworld, y 0 nether/end) with a bonus chest at spawn, problems i am facing from 3 days :

Minecraft doesn't do the load.json until the player does /reload
Nether portals generate on the barrier floor
I fixed the exit portal thingy via making feature in the world gen (oby pillar in the 0 0 chunk) but the problem is the function that removes that pillar doesn't work (I used a advancements (The End?) to run the command or function

Plz help i am getting crazy
1.21.7