Yes I think the question needs to be refined.
The first, and often toughest step, in scientific method is to ask a meaningful question.
Where is this question coming from?
You can electrolyze water at 100 feet - the pressure is only about 4 atmos.
For a given mass of water electrolyzed, the volume of gas that results will depend on the temperature of the gas.
If you are prepared to heat it, then it can have any volume you like.
You do need to expend more energy to electrolyze water at greater depth - precisely because you have to expand the resulting gas bubble against the pressure of the surrounding water. But you could just do the electrolysis in a specially constructed pressure vessel.
The mass of gas will be the same because that depends only on the mass of water you started with.
Once produced, if not kept in a container, the gas will escape and maybe get dissolved into the water before it reaches the surface.
Every now and again, someone figures they can generate power using electrolysis at depth and the natural buoyancy of the gasses.
Perhaps this is what you are wrestling with?