Boxtron is another awesome Steam Play tool! Covered here a few times now, like Proton it enables you to play games on Linux that don't have a Linux build setup on Steam only this is for DOSBox games.
Rather than running DOSBox-powered games on Steam through Proton when they don't have a Linux build of it all up, using Boxtron should give a better experience.
Today a new release went up with Boxtron 0.5.4 fixing multiple issues including: games that use multiple CD images not starting like The Dame Was Loaded (and probably other FMV titles), they tweaked Retro City Rampage 486 to use "aspect=false", several bugs around parsing user-supplied regex for MIDI synthesiser detection were fixed, they also fixed a bug preventing MIDI port detection if there are no soundfonts installed and there's now several fallback soundfont names for various Linux distributions.
Additionally, they have another build of DOSBox Staging up as well. DOSBox Staging is their attempt to improve DOSBox with new features, bug fixes and so on while also getting the patches hopefully accepted upstream to the main DOSBox project.
You can download the releases of either Boxtron and DOSBox Staging here on GitHub. Alternatively, they also now have certain packages setup. If you're doing a manual install you can simply download the release archive, extract it and then place it in (make the compatibilitytools.d folder if it doesn't exist):
Once you reload Steam, Boxtron then shows up as an option to force on a game in the Properties.