pyright is a Python Language Server implementation and as such it needs to access the python libraries installed on the host file-system - this cannot be done with strict confinement even with system-files since snapd does not mount the hosts /usr/share/python3 inside the snaps mount namespace. Neither can we use system-backup there is no way to remap the /var/lib/snapd/hostfs/usr/share/python3 to within the expected /usr/share/python3 etc.
Also pyright falls within the existing category for classic confinement of IDEs/compilers and this is quite similar to historical requests such as Classic confinement request for ccls