This mod has a conflicting mixin into PortalBlock. Briefly analyzing your code, I believe this could be solved by replacing the following method in MixinPortalBlock:

@Overwrite
public boolean createPortalAt(...) {
    return false;
}

with:

@Inject(method = "createPortalAt", at = @At("HEAD"), cancellable = true)
public boolean createPortalAt(...,k CallbackInfoReturnable<Boolean> cir) {
    cir.setReturnValue(false);
}

In your mod I see several instances of using @overwrite. This is bound to cause compatibility issues with mods in the future and generally not recommended. The above replacement should allow the mixins to properly load, at a minimum.

Using version 0.2.
Log: https://paste.ee/p/zwu3x

Thank for your help. I removed this overwrite.

I'm playing with carpet and immersive portals in the new snapshots (20w16a) and they seem to be conflicting again

[Warn] @ModifyConstant conflict. Skipping immersive_portals.mixins_ma.json:block_manipulation/MixinServerPlayerInteractionManager->@ModifyConstant::modifyBreakBlockRangeSquare(D)D with priority 1000, already redirected by carpet.mixins.json:ServerPlayerInteractionManager_antiCheatMixin->@ModifyConstant::addDistance(D)D with priority 69420.

Not sure which mod would need to be changed so I've made an issue on both.