As far as I can tell, there's an issue where, on some hardware, the game will immediately silently crash on startup.
This game is several years old, so the developers seem to have moved on entirely from the game. A patch is probably not likely.

If you aren't able to make it work, the easiest solution is to disable your internet connection. The game will boot fine if the system is offline, but this is obviously a temporary fix that prevents you from saving your progress to the cloud, accessing Discord, etc;.

Therefore, we're going to open Windows Defender Firewall and stop all internet communication for the .exe file for the game. This accomplishes the following;

• The game is solo, so there is no need for internet connectivity.
  
• You no longer need to shut your own internet down every time, just to play a single game.
  
• You can still access other applications such as Steam while the game is running.

There's several Firewall apps on Windows 10 and 11, so make sure you're finding the right one with the full title.


Once you're inside Windows Defender Firewall with Advanced Security,
1. Click "Outbound Rules" in the left pane.
2. Click "New Rule..." in the right pane.
Both options are highlighted below.


In the New Outbound Rule Wizard, choose Program, then click Next.
Now, click "This program path:", and specify the HeartnSlash64.exe file. This should be located in your default Steam installation path, usually C:\Program Files (x86)\Steam\steamapps\common\HeartnSlash\HeartnSlash64.exe.

• Now click Next, and choose Block the connection.
  
• Apply the rule to Domain, Private, and Public networks.
  
• Name the rule anything you choose; I went with "H&S Fix".

If accomplished properly, you should now see the rule at the very top of Outbound Rules.

That should be it; the game is now blocked from internet communications and won't prevent other applications from doing the same.

Why this fixes the problem, I will never know. I'm not too interested in doing anything like packet-sniffing to see what, exactly, the game is trying to read. This solution makes the game playable again, and that's good enough for me.

Many thanks to the people in the Steam Discussions forum for eventually finding a solution to this issue, and I hope it helps many others too.