By "not mainstream approved" you mean it's largely discredited and confined to quacks and charlatans online. Outside of its one legitimate use—very specific cases of epilepsy—no serious medical organisation endorses keto for the general population or cancer patients.
The third video you link is of a person who thinks that they cured their cancer with, among other things, juicing, breathwork, "positive mindset", and keto. This is nonsense.
> despite people healing conditions on it that no modern medicine could
If it worked, it would become "modern medicine". The reason it's not accepted in the mainstream is that it has failed every basic test of efficacy. The reason that you will find it promoted primarily on youtube and not in major medical journals is that the youtube audience is less well-equipped to spot it as snake-oil.