At least this is straightforward. Fresh version of Doomsday 2.0.3 on a recent, up-to-date Windows 10 install. I've had Heretic: Shadow of the Serpent Riders on Steam for a good while, but I still did an uninstall, install and launched it once.
Nevertheless, Doomsday doesn't see an IWAD when I point it at \Steamapps\Common\Heretic Shadow of the Serpent Riders\base . Even though the HERETIC.WAD file is most certainly there. Along with HERETIC.EXE, the dosbox resources, etc..
What should I do (beyond wail in despair and curse the Serpent Riders, of course) ?