I checked the manjaro repo, found out manjaro is installing the extension in /usr/share/nautilus-python/extensions/ .
The extension was there, but it was slightly different from the one in the official repository,
https://github.com/GeopJr/Collision/blob/main/nautilus-extension/collision-extension.py
so I removed it and, by copying from this makefile.patch,
https://gitlab.manjaro.org/packages/extra/collision/-/blob/master/Makefile.patch?ref_type=heads#L11
sudo install -D -m 0644 collision-extension.py /usr/share/nautilus-python/extensions/
reinstalled the version from the upstream repo. Now it works perfectly