UT2004 has a Linux port, I believe developed by Icculus[0] but it's pretty long in the tooth. Requires libc5, an old version of SDL, and OSS for sound.

Regardless, it'll still run on modern systems if you acquire old libc binaries[1] (and preload them), use SDL 1.2 (possibly a patched version[2] which enables Alt+Tab) and start the game using aoss[3] for sound.

[0] https://icculus.org

[1] https://www.unix-ag.uni-kl.de/~deusser/UT2004/

[2] https://github.com/infertux/SDL-1.2.7

[3] https://alsa.opensrc.org/Aoss

I don’t think they ever did. I run mine in Steam using Proton without any configuration minus a widescreen fix, which has actually been a lot easier than trying to get it to work in Windows 10 (I use amdgpu)

It came with the Linux installer on the DVD, same as UT2003.