As stated here on the embeddium side:
embeddedt/embeddium#80 (comment)

• If the player uses Alex's Caves with Embeddium, the depth glass will not function as intended and instead display similarly to normal glass. Embeddium does replace the fluid renderer breaking the functionality of the depth glass. Was stated to post the issue on this mods side.

without Embeddium:

With Embeddium Included:

How has this issue still not been addressed?