I can play Modern Beta, a Fabric mod on Forge via the Syntra Connector mod. Modern Beta is a world generation mod that reverts the world generation to various older versions of MC such as Indev, Infdev, Alpha, Beta, Old Legacy Console, and PE Alpha. I made a new survival world with the Beta 1.7.3 World Generation, and most of Alex's Mobs entities spawn normally in the beta biomes except the Giant Squid. They spawn too close to the surface, and I doubt that this is an intended feature, because isn't the Giant Squid supposed to be a rare mob found in Deep Oceans and not in puddle-deep bays or rivers?

Steps to reproduce:

1. Install Modern Beta and Alex's Mobs for 1.20.1 with all of their dependencies.
2. Create a new world with the Beta 1.7.3 world type.
3. Find a body of water and wait for a Giant Squid to spawn.
   EDIT Before anyone comments, no, this is not a normal Squid that was struck by lightning.

The same applies to Frilled Sharks. They spawn very close to surface water.

Another Modern Beta and Alex's Mobs conflict: Skelewags do not spawn at Shipwrecks in Beta 1.7.3 worlds. They are not disabled from naturally spawning as well.

Update: The same applies for Underminers in Mineshafts with Beta 1.7.3 worlds.