You haven't specified if you want a realistic or more fantastical answer. My answer is in regards to a Mini-Neptune, not a Super Earth, so keep that in mind.

The realistic answer is you wouldn't have a 'surface' as you think of it. If the planet is large enough to accumulate hydrogen/helium, then it won't have a defined 'surface' as you think of. True, oxygen is denser, and will clump further towards the core, however, we have these things called molecules which are combinations of elements that may weigh more, like water.

Mini-Neptune is a term that is somewhat used in tandem with Gas Dwarf, however, it emphasises a smaller ice giant moreover than a gas giant.

  This means your upper atmosphere will be mostly hydrogen/helium, quickly followed by a large majority of your planet being composed of ice or water (or ammonia, or a myriad of other chemicals, but lets stick to Earth analogues for now).

From there, your 'solid surface' would instead be more like layers of an ocean, with a helium/hydrogen surface, mixed water, followed by denser or more pressurised ices. Think like the abyssal plain or ocean trenches. Now, all of this would be pitch black, no light at all would reach past the hydrogen layer, but you still could technically have life... maybe... through chemosynthetic reactions, think deep ocean monsters and tube worms and whatnot. There is the temperature to think about, all that pressure is going to cause an awful lot of heat, and your planet doesn't have a tectonic 'crust' per se to isolate volcanism, it's possible your 'ocean depths' might function more like a transition from thin water, to thick water, to watery magma, to actual magma. But again, there's nothing technically stopping you from developing a workaround, just a lot of improbability.

The fantastical answer is you can do what you want. Put a dome around it or something, there's an air pocket, or maybe the entire ecosystem is in the stomach of a large fish, it don't matter. You can make up what you want, the rule of cool reigns supreme in science fiction.

You haven't specified if you want a realistic or more fantastical answer. My answer is in regards to a Mini-Neptune, not a Super Earth, so keep that in mind.

The realistic answer is you wouldn't have a 'surface' as you think of it. If the planet is large enough to accumulate hydrogen/helium, then there is no point within its mantle at which matter suddenly 'becomes solid'. True, oxygen is denser, and will clump further towards the core, however, we have these things called molecules which are combinations of elements that may weigh more, like water, and this may shift the balance.

Mini-Neptune is a term that is somewhat used in tandem with Gas Dwarf. However, it emphasises a smaller ice giant more so than a gas giant (which is mostly only hydrogen and helium). This means your upper atmosphere will be hydrogen/helium, quickly followed underneath by a large majority of ice or water (or ammonia, or a myriad of other chemicals, but lets stick to Earth analogues for now).

From there, your 'solid surface' would instead be more like layers of an ocean, with a helium/hydrogen surface, mixed water, followed by denser or more pressurised ices. Think like the abyssal plain or ocean trenches. Now, all of this would be pitch black, no light at all would reach past the hydrogen layer, but you still could technically have life... maybe... through chemosynthetic reactions: deep ocean monsters and tube worms and whatnot. There is the temperature to think about, all that pressure is going to cause an awful lot of heat, and your planet doesn't have a tectonic 'crust' per se to isolate volcanism, it's possible your 'ocean depths' might function more like a transition from thin water, to thick water, to watery magma, to actual magma. But again, there's nothing technically stopping you from developing a workaround, just a lot of improbability.

The fantastical answer is you can do what you want. Put a dome around it or something, there's an air pocket, or maybe the entire ecosystem is in the stomach of a large fish, it don't matter. You can make up what you want, the rule of cool reigns supreme in science fiction.