Glad you asked! The N64 is one of the aforementioned difficult cores that are actively being worked on. There are a couple of bounties to update the main Mupen64 Plus core from RetroArch, and another to work on the recently released 64-bit ARM dynarec for Mupen64 Plus (and Parallel), which can now be tested out through the nightly downloads! A dynamic recompiler (dynarec) allows instructions to be translated ahead of time from the N64's native MIPS architecture to the native format of whatever platform is doing the emulation. This eliminates a lot of emulation overhead and makes for
significantly faster emulation.
Do you want to help with the development of both the Mupen64 Plus core update and also the 64bit Mupen64 dynarec?
You can give your support to the current developer in charge of it!
@m4xw is the developer that is constantly updating everything Nintendo 64-related on the Switch release of RetroArch, so if you want to continue seeing great updates for this core, be sure to support him through his Patreon:
https://www.patreon.com/m4xwdev
You can check the current and most up-to-date build in the
Disclaimer section of this very post.
If you want to see full-speed N64 emulation on the Switch, why not throw in a few dollars to show your support?