First of all, make a copy of the entire LUN (if possible) using trivial disk cloning or P2V software like Microsoft Disk2VHD https://aka.ms/disk2vhdor free V2V Converter https://www.starwindsoftware.com/starwind-v2v-converter to avoid damaging your only copy even further.
After that part is done, proceed with using ReFSUtil and perform a quick scan of your damaged LUN to see if that helps. You should get a list of recoverable files.
If a quick scan does not find anything, proceed with a full scan. Depending on your LUN size, it may take a substantial amount of time, so it would be best to leave it running overnight. Make sure you have enough free storage to copy recovered data to.
More information about using Microsoft ReFSUtil can be found here https://learn.microsoft.com/en-us/windows-server/administration/windows-commands/refsutil.