Yes. Fugue is free to download from Modrinth. Its license is GPL-3.0-or-later.

How do I add it to my Nxeon server?

Use “Add to a server” on this page, or open NxLabs from your dashboard. We install it, restart your server and switch it on.

Fugue — Minecraft Mods | NxLabs

From Modrinth

Patch mods for Cleanroom

Fugue is a patch mod for Cleanroom, it patches most of the incompatibilities between existing Forge mods and Cleanroom.

With this mod, migrating from Forge to Cleanroom is seamless. Every patch is configurable!

FAQ:

Q: What is Cleanroom?
A: Cleanroom is a 1.12.2 Forge fork, providing newer toolchain, new APIs and 99% compatibility. Our plan is to make 1.12.2 up-to-date with latest toolchain while adding more feature to Forge & vanilla, so we don't need to care about higher versions' X point release * Y Mod API headache.
Q: How to install Cleanroom?
A: Please follow the instructions in README.
Q: Can I include this in my Forge modpack? Will it crash my Forge pack?
A: Yes, you can, and it is safe! This mod won't be loaded or crash anything in a Forge environment.
Q: Java version?
A: 21 or 22. We are planning to support development using latest LTS version Java and running with latest Java.
Q: Current state?
A: Cleanroom have reached well usability, many small and large packs have been ported to Cleanroom after some tweaks, even SpongeForge has a solution. But we are lacking manpower, please join our Discord if you are willing to help.

Note: mod files marked as "Forge" because CurseForge doesn't support Cleanroom yet.

Patched mod list(outdated):

From source data

Built for Minecraft 1.12.2.

Runs on Forge.

Rated a light load on a server.

From the catalog

Listed on Modrinth as “Mods”

New mechanics, content and overhauls that change how the game plays.

From source side support

Modrinth lists Fugue as required on the server. Check its Modrinth page to see whether players need it too.