I have looked online for possible answers about this, but I can't get this to launch.
I'm on Void Linux with glibc, x86_64.

log.txt:
Running Barony
[14-27-56] Data path is ./
[14-27-56] Data path is ./
[14-27-56] Output path is /home/kenny/.barony
[14-27-56] Output path is /home/kenny/.barony
[14-27-57] rng not seeded, seeding by unix time
[14-27-57] rng not seeded, seeding by unix time
[14-27-57] keyboard bindings for player 0
[14-27-57] keyboard bindings for player 0
[14-27-57] Unable to open file '/home/kenny/.barony/config/config.json' for read (2)
[14-27-57] Unable to open file '/home/kenny/.barony/config/config.json' for read (2)
[14-27-57] [PhysFS]: successfully initialized, last error: no error
[14-27-57] [PhysFS]: unsuccessfully mounted holiday .//themes/merry/ folder. Error: not found
[14-27-57] Critical error: 13
[14-27-57] closing engine...
[14-27-57] freeing engine resources...
[14-27-57] freeing ui resources...
[14-27-57] [Text Cache]: dumping...
[14-27-57] freeing map data...
[14-27-57] freeing textures...
[14-27-57] freeing sprites...
[14-27-57] freeing models...
[14-27-57] freeing sounds...
[14-27-57] closing network interfaces...
[14-27-57] shutting down SDL and its subsystems...
[14-27-57] [directoryContents()] Failed to open directory "/home/kenny/.barony/logfiles/".
[14-27-57] [PhysFS]: De-initializing...
[14-27-57] notice: archiving log file as /home/kenny/.barony/logfiles/log_20231213_142757.txt...
[14-27-57] success

The other linux topics here address other issues. I have yet to find a "themes" folder or that "merry" folder, not sure where that is. I emailed the developers and will update here if they send something back.