I have been looking to make some simple homebrew apps on Nintendo Switch using Python. As far as I know PyNX (Python 3.5 for the Nintendo Switch) exists and I have tried it but ends up crashing on the latest Atmosphere release + HOS release.
Any alternatives to PyNX?
No, its only for Nintendo Switch (Likely due to the fact, its made around the Nintendo Switch's API .etc.)
You would much better off using a screen recording app.
You should update to OFW 13.2.1 and Atmosphere 1.2.6.
Second, I highly doubt game performance has to do anything with installing another OS onto the switch.
Hekate has the option to boot into OFW.
I would suggest to boot into Hekate and boot into OFW. Hold the Power Button for a few seconds to force shutdown the Switch.