Playing on linux

First, you have to set up Lutris itself. It'll make working with Windows games a heck of a lot easier in the long run since it handles most of the rough parts of working with Wine:

• Install Wine and Lutris on your system. Instructions vary depending on the distro, but the package names should be similar to that (possibly exactly that, actually).
• On Lutris, click the three-dot button on the top-right, go to Preferences > Runners, scroll down to Wine and click the rightmost button.
• Download wine-ge-8-25, it's basically a version of Wine with all the niceties from Steam's Proton (you'll still need the system version alongside it, though, according to the Lutris site).

Now to set up niceRO:

• Download the niceRO zip file, create a folder named niceRO, unzip the contents there. If you get permission issues extracting the niceRO_client folder for some reason (happens sometimes, zip files on linux are weird), run chmod -R 700 niceRO_client.
• Lutris options
  • Click the top-left plus icon.
  • Choose Add locally installed game.
  • Name it niceRO for now and choose Wine as the runner.
• Game options
  • Executable: Ragnarok.exe
  • Wine prefix: the folder you unzipped niceRO_client into (niceRO)
  • Prefix architecture: 32-bit
• Runner options
  • Wine version: wine-ge-8-25.
  • Enable the following:
    • DXVK
    • D3D Extras
    • Esync
    • Fsync (if available)
    • FSR
• System options
  • Disable Disable Lutris Runtime.
  • Enable Prefer system libraries.
  • Click Save.
• In Lutris, click on the niceRO entry, hit the arrow next to the wine glass icon, choose Wine configuration. On the Applications tab, go down to Windows Version and choose Windows XP. Hit OK.
• Same arrow as before, choose "Run EXE inside Wine prefix", choose "Setup.exe". Configure to your liking.

After all that, just double-click on niceRO or click on Play to start Ragnarok.exe and get going.