Quick answer: NonSteamLaunchers v4.2.94 adds an ARM64 installer for SteamOS ARM64 and ArmadaOS, Heroic Games Launcher and Prism Launcher support, FEX fixes and an NSL entry in the Steam menu.
NonSteamLaunchers, the community script that installs other game launchers and adds them to Steam, now runs on ARM64 devices. Version 4.2.94 went up on GitHub on October 29 and adds support for SteamOS ARM64 and ArmadaOS.
The ARM64 version comes as its own script and desktop file, NonSteamLaunchers-arm64.sh and NonSteamLaunchers-arm64.desktop. The release notes say both the desktop version and the Decky plugin should now work on ARM64 devices. Contributor indiesaudi added the ARM64 support, along with Heroic Games Launcher and Prism Launcher support and fixes for FEX, the tool that runs x86 programs on ARM.
The update also adds an NSL entry to the Steam menu in Game Mode. It opens a settings page with the scanner and boot video options, and the developer says more settings are coming. PokéBonk was also added to the list of streaming sites.
Steam Deck HQ and PC Guide both point out that ARM support could open the tool up to more hardware, such as ARM handhelds running these systems, and both name Valve's Steam Frame as one possible example.
If you already have NonSteamLaunchers installed, Steam Deck HQ says running it again updates it to the latest version. My non-Steam launchers guide walks through the setup on Steam Deck.