The error "Python XX dll could not be loaded - check executable in your pyxll.cfg" when loading the PyXLL add-in is most often caused by a mismatch between the version of Python you are using and the build of the PyXLL add-in.
The PyXLL add-in is built for each different version of Python. All current versions of Python are supported (and most older versions too), but you have to have the correct build of the PyXLL add-in to match your Python version.
The easiest way to get started is to run "pip install pyxll" followed by "pyxll install" and let the install script download the add-in for you by selecting "n" when asked if you have already downloaded PyXLL. If you select "n" it will download the right file for you.
If using a virtual or conda env, make sure you have the virtual or conda env you want to use active before doing this.
If you downloaded the PyXLL add-in manually from pyxll.com/download.html, you need to select the correct version of Python where it asks what version of Python you are using. You will then be given the correct build of the PyXLL add-in to match your Python version.
You can have multiple copies of PyXLL on your computer at the same time and can use the "pyxll activate" command to switch between them (https://www.pyxll.com/docs/userguide/installation/cli.html#pyxll-activate). This is useful when working with multiple different Python versions.
If you are switching to a different version of Python and want to keep your PyXLL environment the same, you can download PyXLL for the version of Python you are using and replace your existing pyxll.xll file with the one for that version of Python manually. After replacing the pyxll.xll file, you only need to update the executable setting in your pyxll.cfg to point to your new Python environment.