Through careful examination of multiple strongholds, I have been able to observe that they generate very near to the ocean’s surface and occasionally partially above. In almost each case, a layer of material (most often stone and over 10 layers thick) surrounds the structure as to cover it. However, this generation around the stronghold is unnatural looking as sides do not have smooth gradients and rather are visibly chunky, climbing two blocks vertically before having a setback of one. This can be seen in the screenshots provided. Furthermore, in one observed instance, this generation failed in part, leaving a partially covered stronghold with the rest being exposed. In this, visible generation errors can be seen where the surrounding blocks failed to generate leaving straight edges. It should be noted that a stronghold could not be observed to be sufficiently below the ocean’s bottom as to not be seen. On Java strongholds are able to be generated much deeper (and in my testing down to deepslate) yet, on Bedrock, the strongholds in oceans appear to be located on the same or very close y coordinate which is also the same y coordinate as the ocean floor. I will make clear that I do not know how it is supposed to generate, however, the current process does not conceal the stronghold. This is both with it’s layered covering and with its high y coord positioning.

Seed: 2345

Coords: (14925, 71, 4355) (-10737, 77, 8229) (-2359, 66, 21063)

To reproduce:

1. Create new world using provided seed above.

2. Teleport player to one of three locations provided above.

3. Observe the clear presence of an anomaly on the sea floor when examining the terrain generation. 
4. Upon closer inspection, the oddly shaped generation covers a stronghold.

Note: The first stronghold is completely covered and outlined in red, the second is situated in a coral reef (one picture of this has a cut out demonstrating the stronghold under the material), and the third possesses land on the surface of the water, is only partially covered, and also has been outlined in red.