Cheers! I've attached two small ZIPs for Ikaruga, one for the MiSTer and one with the PC settings and instructions.
You'll need the PC launcher:
https://github.com/BossRighteous/GroovyMiSTerCommand/releases
You'll also need the GroovyMiSTer-compatible RetroArch build and Flycast core. I'm using Windows, are you running Windows on your Steam Deck too, or SteamOS? I've included examples for both, but only my Windows setup has been tested.
Change mister_host in the launcher config and mister_ip in the RetroArch config to your MiSTer's IP, then update the emulator and game paths.
For multiple cabinets, the idea would be to run a separate launcher and emulator instance for each MiSTer, each configured with its destination IP, without needing VMs. I haven't tested them simultaneously yet, so you'd need to check for port conflicts and make sure each launcher only manages its own game. But in theory, if you have 4 MiSTers each with their own IP address, then on your PC you'd have 4 listeners, each listening to the instructions/games to play
Give it a go and let me know how you get on!