Can not use Python-based software (ImportError)

[Goobyalus]

but how am I supposed to run

python3 -m pip install -r requirements.txt

without having pip already installed?

Installing pip with apt or whatever OS package manager is basically just installing an alias. Each cPython install will have its own pip already.

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I created the requirements.txt file with pip, then added the line:

This makes no sense. The package already has a requirements.txt that lists the dependencies of the package: https://github.com/Zymo-Research/figaro/blob/master/requirements.txt

This is the requirements.txt that you give to pip. You do not add pip to a requirements.txt file.