Related to MC-238977, which was fixed on Java 1.18.2 (parity issue).

Currently, on Bedrock, glow squid can spawn anywhere between Y=-64 and Y=30, as long as it is underwater and underground. However, by game definition, underground requires any block above full water block to have glow squid to spawn. This means if you have a lit-up water chamber in the flat world where it is generated below Y=0, the glow squid will spawn regardless of whether you put up any light blocks or not.

On Java, this issue was fixed in 1.18.2 by introducing changes where glow squid would only spawn in complete darkness or light level 0.

How to Reproduce
1. Create a flat world.
2. Fill a 20x20x20 water block.
3. Put a layer of stone above the water.
4. Lit up the water chamber with any light block.

Observed Result
The glow squid will spawn regardless of light.

Expected Result
The glow squid shouldn't spawn, unless it is in complete darkness.

Quick update: Added the world download to test the glow squid spawning. This can be tested in 1.18.20.29/30 beta/preview, however, you can repro yourself by following the steps above.