In the 1.18 update, you can find structures below y=0 such as dungeons and mineshafts. However, strongholds cannot be found below y=0. This is already a feature on Java, so this can be considered a parity issue.
Step to Reproduce
1. Create a new world.
2. Do /locate stronghold and teleport to that stronghold.
3. Check if it's generating below Y=0/on negative Y levels.
4. Repeat this from step 2 but by teleporting away from the previous stronghold.
Expected Result
Some of the strongholds are generating below Y=0/on negative Y levels.
Observed Result
None of them are generating below Y=0/on negative Y levels.
Confident this is a bug not a parity issue because sometimes Eyes of Ender will lead you to a location where the Stronghold should be and there's nothing there. Presumably because it was supposed to generate below Y=0 and...didn't.