sbt 1.4.4 with IntelliJ: Extracting structure failed

I am getting a rather strange error when trying to use the IntelliJ built-in sbt-compiler to open projects with sbt 1.4.0 or higher:

Everything works fine for projects configured to use sbt 1.3.x or lower. In this example, I was trying to open the ScalablyTyped Demo project. The same keeps happening with other projects as well. I upgraded my IntelliJ to the Community 2020.2 version and the Scala plugin to version 2020.2.49, but to no avail.

Compiling the projects with the built-in sbt shell works, so it seems to be a problem of IntelliJ itself. Any hint would be greatly appreciated.

Edit 2:

This seems to be causing the error, but I have yarn installed and can use it in a cli, so that is rather surprising:

* Welcome to ScalablyTyped demos!
*
* For documentation see https://scalablytyped.org .
*
* Note that the first time you import/compile the projects it'll take a while for the dependencies to build
*
[info] set current project to demos-master (in build file:/C:/Users/baierlf/Downloads/Demos-master/Demos-master/)
[error] stack trace is suppressed; run 'last electron / externalNpm' for the full output
[error] stack trace is suppressed; run 'last electron / ssExtractDependencies' for the full output
[error] (electron / externalNpm) java.io.IOException: Cannot run program "yarn" (in directory "C:\Users\baierlf\Downloads\Demos-master\Demos-master\electron"): CreateProcess error=2, Das System kann     die angegebene Datei nicht finden
[error] (electron / ssExtractDependencies) java.io.IOException: Cannot run program "yarn" (in directory "C:\Users\baierlf\Downloads\Demos-master\Demos-master\electron"): CreateProcess error=2, Das     System kann die angegebene Datei nicht finden
[error] Total time: 3 s, completed 01.12.2020 15:42:43
[info] shutting down sbt server

Translation:

German: Das System kann die angegebene Datei nicht finden

English: The system is unable to locate the file

Edit 3:

I can run the yarn command, when doing it manually: