Issue occurs on the latest version of Immersive Portals and DOES NOT occur if you generate terrain normally. However, should you use the 1.18 generation data pack preview available from Mojang here then bedrock generation does not get replaced with obsidian as shown in the image below:

Currently, no other issues have been encountered. Other than the unstable build warning upon world start being a tad annoying as it cant be suppressed in the config it seems.

This is because that the bedrock replacement code hardcoded the y range. Now fixed