Proton is really a WINE fork intended specifically for Steam games. Most of the changes in it target games.

WINE might be able to run the program, would be what I’d try.

Or you might be able to run a Windows VM on newer hardware and run it on that, would be my fallback attempt. Less seamless than just having a Windows program open a window alongside Linux ones, but sometimes that can work if WINE can’t do it.

I’d see if Linux can recognize the label printer, if this is really ancient hardware. That’d be my first step. Then look into having apps print to said printer.