Many alien worlds will most likely be water worlds. I was wondering what the deepest possible global ocean dept is where land is still possible. I think that volcanic islands will still have a chance to form even after continents are no longer possible since they can have quite steep slopes which are supported by water. I'm aware that this isn't anything we can describe easily, so all I'm looking for is a rough estimate. Would there be any reason not to scale this estimate linearly with gravity to adapt it for worlds with nonterran gravity?
On Earth, the deepest point in the ocean is Challenger Deep (36,200 feet) and the tallest mountain is Mount Everest (29,029 feet). Mount Everest is roughly 65,000 feet taller than Challenger Deep, so if you parked the two next to each other and raised the ocean levels to just below Everest's peak (RIP life) you could have an ocean more than 12 miles deep. There's no hard and fast reason that the difference couldn't be even greater in your fictional world.