Swimming pools are normally constructed empty. They were withstanding surrounding soil before they were filled, and concrete strength increases with age (for about 90 days, typically). On the other hand, a sunken structure like a pool that is roofed over, becomes a "confined space". Unlike a typical structure, heavier-than-air gases cannot escape from the pool. Such gases could originate from the drain system or flow from leakage outside the pool area. For examples, leaking propane or various gases from sewer lines in the vicinity. A sunken greenhouse would almost certainly be a building code violation for that reason. If you build it, ventilate it by means both active and passive and do not enter if you can't verify that ventilation is working.

Hmm, it would seem to me that pools that break when empty should be rather rare as that that is not a sound construction in general. Maybe in costal areas with raising groundwater table due to sea-level rise it might happen though.

Edit: the lifting issue is somewhat common with underground cisterns and septic tanks though, which are typically expected to be always filled with water.

If the pool has a deeper section it could be used as a pond that acts as additional thermal buffer and a sump pump with float switch could make sure the pool doesn't get flooded during heavy rainfall.

If the soil is dry enough to avoid liquefication, lifting should not happen. A ditch around the pool with drainage to lower ground at some distance would likely solve the problem even if the soil is problematic.

If the concrete is reinforced with rebar, it can withstand sideways load by the soil. If not, the issue of soil pressure would need closer consideration.

Disclaimer: I'm not an engineer