Hydr8gon has released a DS Emulator for the Nintendo Switch:

I present to you my port of melonDS to the Switch. It's nothing fancy, so don't expect too much. All the basic features are there for it to be usable. The file browser is very rough, and the emulator is slow.

I'll answer some questions here because I know they will be asked:
Q: Is this the same build you posted in the original DeSmuME-NX thread?
A: No. Since then I have ditched SDL2 and redone my port from the ground up. This build is significantly faster than the old one.

Q: Is this faster than DeSmuME-NX?
A: Not yet, no. But in the games I tested, it's not far behind.

Q: Is there OpenGL support?
A: No, not yet. melonDS does not have a hardware renderer, but when it gets one, I will add it to the Switch build.

Q: Do I need BIOS files?
A: Yes. Dump the files from your DS and place them in 'sdmc:/switch/melonds'. Make sure they are named 'bios7.bin', bios9.bin', and 'firmware.bin'.

Q: Where do I put my ROMs?
A: Anywhere you want. The file browser supports navigating directories.

Q: What's the point?
A: StapleButter (melonDS developer) has resumed working on the project. As melonDS improves, I will update this build. Hopefully, it'll eventually reach full speed on the Switch.

download https://github.com/Hydr8gon/melonDS

via https://www.nintendomax.com/viewtopic.php?f=168&t=16798