Disclaimer, I also use these ideas in my own stories but you are free to borrow them.
Ogres could be from a unique jungle or forest where the trees have plenty of food to maintain their large size. Their original habitat is in an area that has trees which can filter water as mangroves do because its biome is on a lowland area which the seawater floods up its river delta and into marshland and swamps that make the foundation for the biome.
They'd be herbivores since most large animals tend to be eg. rhinos and elephants with the exception of whales which are carnivores.
But you could make them omnivores if you want them to be more hostile and perhaps historically in times of famine they had to eat animals to stay alive.
The ogre would be a feminist system where the females rule since hight plays a lot into the evolution of humans social status which is along with endurance a lot of the reason males have dominated leadership and laws throughout history. In ogre coitus, the females would be on top.
Since in your story the ogres can drink seawater they'd have to have an extra hole with a semi-permeable membrane on their face so they can perform osmosis. On the outside of their body like where fish have their gills. Not on the inside of their stomach since that would just give them a leaky gut.
Since they have large expandable stomachs they would have a very slow digestive system to ferment and break down their food. Which would consist of raw flora and meats. They would not cook their food since that would mean the food would already be partly broken down and you may get lean Ogres. If the ogres can refine their food like in bread or something they would end up metabolizing it to fast and you would get diabetic ogres. Or who knows that could be a plot point.
Since they have a lot of blubber this would be to last hibernating in winter, travelling through snowy mountains to reach another prosperous oasis they can have their young. Or even for surviving long periods of time floating on their backs in the ocean before they reach new islands, they can colonize. This would also make sense since their solitary and after the offspring are born the farther could quickly yeet out of there and leave, leaving the mother to bring up the young vice versa. Then after they have leant the ogre how to survive and traditions the young would leave on their own journey for adventure and love in a distant land.
Bipedal depends on if they have to use their hands often for climbing or lifting or digging or if they've been taken up with wings in the case of a bird.
Since they live so long they'd end up breeding very late into their life and very rarely since that would increase the evolutionary pressure for evolution to program them in a better way to increase their immune systems and have a lower risk of cancer, cellular senescence removal of tau and amyloid-beta proteins in the brain as well as increasing the longevity of their telomeres and repair of double-strand DNA breaks increased epigenetic stability and maintain their glycans for longer.
They would be able to see colours as we do so they can find the right plants to eat. Since they are solitary nomads they could have a long-distance row to let other ogres know where they are and if their a potential mate or if their in conflict with a stronger predator.
Their sense of smell could be reduced due to them living in very foul-smelling swamps with a lot of rotting organic matter or other intense smells.
If they're not from the same genus as humans and are thousands of years apart and you want ogres to be able to cross-breed they'd need to have a close enough genome and epigenome. As well as their immune system would need to be excepting of the other species seed or they would have to be immunocompromised maybe by having their immune system knocked by some kind of antibiotic so they can perform successful coitus.
I don't know much about reproduction so I may go a bit owo, but the ogre's sperm could have evolved some kind of adaptive capabilities similar to antibodies in its way of connecting their glycocalyx's glycans to the eggs
I don't see why that last part would evolutionarily happen unless the female ogres mutated some kind of counterintuitive antibodies that try to attack the sperm and build resistance before it reaches the egg.
I wanna also talk about other fantasy species which seem like they'd be from the same evolutionary genus.
If orcs evolved naturally not being some tormented elf or something they would have more or less the same evolutionary path humans did starting off being hunted by other predators but then evolved a larger brain to outsmart them, so eventually they'd build tools so they could fight and eating them which would also serve as a catalyst for their more primal and violent nature. Orcs probably wouldn't be able to see many colours since humans evolved that for seeing fruit and vegetables.
Goblins could have developed around a place where food was scarce so they evolve to be smaller, breed large litters when the season is right and be less intelligent and have shorter lives since they would have had no evolutionary pressure for longer life spans and instead opt for a more disposable soma.