Seems to work great on RPCS3 for most people with high end hardware. I haven't tried since last year; back then my Ryzen 3600 and Radeon 5700 XT combo was too new/unsupported and crashed constantly even with Vulkan. I should try again, I would expect by now they've sorted everything out.
Edit: Tried it tonight and it seems to work more or less perfectly, aside from some fps drops when you roll through barrels (basically anything that uses Havok). Not sure if I can fix that by playing with settings, from what I understand it should really only affect 4 core / 4 thread CPUs and my 3600 is 6C/12T. Also mods can and should be used with Demon's Souls on RPCS3, IIRC the ones I have installed are high res font, Boletaria Reborn (2.1 Vibrant), and grey line removal. There's also a mod to add Monk's Head Wrappings for offline play and another called Unofficial Patches (Monk's Head plus also increases Pure Bladestone drop rate and lets you fat roll in 5-2). All available on Nexus.