Looks like a fn 1900 holster. War time.
Compare to https://pre98.com/shop/exceptional-...duction-widely-used-in-wwi-beautiful-example/
That's because there were quite a few variations including how the closure was done - over a dozen different shops were making them, but the double mag pouch is the giveaway imo.Close but not identical. I will go with that for now. Anyhow any pocket pistol will seem to fit.