Huh. Seems that no engine folder existed. I redownloaded and installed, and this time an updater downloaded v1.5.3? (sorry, not sure about the last number) from GitHub, and now it seems to work just fine. It seems likely that when BitDefender Antivirus went full potato quality and deleted all the games I had right after I extracted them, it must have also deleted the engine folder right after I installed RPGPM the first time, possibly because it contained JavaScript. I switched back to Avast a few days ago and RPGPM now works just fine! Thanks for your help!