Yes, I go significantly deeper. You seem to be a little confused about how oxygen toxicity works but rest assured that we're aware of it and use appropriate breathing gasses for the depth.

I understand that an Apple Watch Ultra can't be used for those dives, and that's fine — they don't need to support every possible niche use case. But competing smartwatches from Garmin and Suunto do handle deeper dives and the associated gas mixes. There's nothing stopping Apple from doing the same if they want to.