I would like to share a thought (based on canonical information as much as possible) about healing by the Force seen in Ep9 and which has caused so much discussion.
I have always thought of it as very simple: the ability to heal is achieved by mastering the Living Force (which is one of the two aspects of the Force, the other being the Cosmic Force) and learning to "channel" it. As I understand from the prequels, the study of the Cosmic Force was very prevalent, while the study of the Living Force was lapsed and followed by a minority current of Jedi (e.g., the very first dialogue between Qui-Gon and Obi-Wan in Ep1). One aspect of mastering the Living force is maintaining one's self-awareness even after death (thus being able to manifest as a Force ghost), another may well be the ability to elicit healing from physical damage in living tissue. Anakin could not save his mother because, while potentially powerful, he knew nothing about it. Even Sidious did not know about it, which gives me pause as to how even the Sith as far as studying the Force were no better off than the Jedi, although then he must have learned something because in Ep9 he manages to absorb the Living Force from Ben and Rey to toughen his decaying body. While in the Ahch-To texts Rey found the ancient indications to that effect and learned it (and perhaps Plagueis similarly, or re-discovered it on his own). In Yoda's species this ability might be innate (Grogu heals Karga) but after a very long time spent considering almost only the Cosmic Force the master almost forgot it. Am I making it too simple? 🙃
Force healing was extremely inconsistent through SW canon and EU, from making natural healing faster up to basically D&D healing spell Grogu used. I would guess all of those are real because force don't have a spell cards so even powerful master like Luke could only slightly speed the healing because nobody told him any other was is possible, while Grogu just wanted it to heal and the force responded.
More interesting factor is the dark side. I remember the ancient setting of Je'daii in Tython which was explored briefly before the old EU ended, it was well before the schism so they used both dark and light side, and guess what they used for healing: dark side. Specifically the skill that would later be known as the sith alchemy, and it was very effective. Logically, dark side would be way better than light side at healing, because dark side directly tampered with life. I wonder what exactly Grogu used :)
