Managed to get the game running by building an empty project in unity, and transfering that dll to the download folder - It's just unityengine files after all (as far as I know), while the source code is contained within the download. For those who want to do the same without an instant error on startup, you can either take the dll out of any unity game that's built in version 2019.4.3 with x86_64 architecture, or plop this file into the game folder: https://drive.google.com/file/d/1Xi12QyrMOywmmQ_kc32EDJwsLxwjeuV_/view