The Switch scene never really sleeps and while we’re waiting for CFWs like Atmosphere to be updated with FW 9.0.0 support, Hydr8gon went ahead and released melonDS 0.8.3 for the console. This update is mostly a bug fix update, more about which can be found here, so it’s important not to expect an awful lot from it but it has a couple of accuracy updates and a fix relating to audio output which might be useful for some games.
That being said, some significant performance improvements to melonDS on the Switch may be coming in the future as GBATemp user ‘catlover007’ is currently working on an ARM64 JIT for the emulator which would greatly reduce the strain on the Switch’s CPU. Some more information about this can be found in these comments (comment 1 | comment 2).
To grab the melonDS 0.8.3 NRO for your Switch, follow this link to its GitHub release page and remember, many DS games may run slow or require you to overclock your console for playable frame rates.