It looks like you have a Pangaea-style super-continent, so it must be either very early or very late in your world's history.
It also looks like your super-continent has a big chunk bitten out of it, like a meteor impacted there and left a very large crater to be filled by the ocean.
I started off using Fractal Terrains to generate the land. When I found a shape I liked, I started tweaking the settings particularly climate and temperature since I didn't like the initial offering of a frozen world with a small band of warm at the equator. I do need to redo the legend in the corner, since the planet is quite a bit bigger than it suggests. Basically around the size of Mars with a higher iron content for a gravitational pull closer to Earth's though I haven't done the math yet. I could probably use GURPs Space to work it out, the only GURPs book I really ever used.
I had considered more than one continent but I really liked the shape I got. As you may know, Fractal generation is automatic. Sure I could draw my own world, but getting those nice maps with rainfall and the like wouldn't be possible and the idea is to make something I actually might use and/or share in some form or another. The shape kind of reminded me of a Phoenix so I kept it.
It looks like you have a Pangaea-style super-continent, so it must be either very early or very late in your world's history.
There are other options. Such as the planet is engineered (how meta!) or it was reshaped in some catastrophe.
It also looks like your super-continent has a big chunk bitten out of it, like a meteor impacted there and left a very large crater to be filled by the ocean.
My tentative story is that the planet's resident ancient species had some horribly cliched experiment which destroyed a good chuck of the planet millennia ago. Their descendants somehow survived in that island in the middle, protected by superior materials that comprise the arcology they live in.
I mentioned the inspiration would be Moorcock, though I am not sure how many of the tropes I want to use. There will definitely be elves and they will mostly certainly be Melnibonean style jerks, with some inspiration drawn from the highly militant Imperial Elven Armada from Spelljammer. I am tentatively working on it for D&D 5e, though scaling it down for an OSR would be easy enough. Less races, less classes. It might be easier to just focus on core races along with one or two extras.
One thing I'd like to avoid is Tolkien tropes. That is easy enough since I never really got into Tolkien. Still there has to be something for potential players and DMs to connect to. But it's not like I care if I publish it or anything so I'm not in a hurry. I mostly just like to play with maps. I have a few samples
here.