This anon has researched Cathars at length.
Look into Albigensian Crusade.
Reports of over 1M Cathars slaughtered.
Cathars had elements of Buddhist approach to religion.
Experienced lay people were considered teachers.
Believed in the concept of relative and absolute reality.
God is inside.
Through mediation one comes to the absolute knowledge of reality.
Reality is an illusion (relative reality).
Absolute reality is the "big mind" or as Tibetan Buddhist call it Rigpa.
That which can not be described or pointed to.
Cathartic approach to religion posed a threat to the Catholic Church.
Priests were losing control.
https://en.wikipedia.org/wiki/Albigensian_Crusade