OpenRPA uses embedded python. It currently only supports python 3.7 so it has one builtin. You can install packages using the pip install activity in openrpa, or you can install it your self from a command line at
C:\Users\%USERNAME%\AppData\Local\python-3.7.3-embed-amd64
If you go to settings → recorder extensions → scripting you can disable/enable using the builtin, or the one you have in your %PATH% environment variable. But if you switch to your locally installed one, it MUST be version 3.7 ( this can be needed if you need to use UI libraries, since TK is missing from the embedded version )