I think YouTube are in charge of their own platform, and if they don't want it to be used as a platform for amplifying dangerous misinformation that will result in lives needlessly being lost, they're free to act accordingly. And if they want to use the WHO as a basis for reference for doing so, that's a sensible approach.
As for the WHO advice, let's take the mask example. It's being presented incorrectly in this thread. The WHO advice, as I linked to above, is that wearing medical masks "is one of the prevention measures that can limit the spread of certain respiratory viral diseases, including COVID-19", but caution that "the use of a mask alone is insufficient to provide an adequate level of protection, and other measures should also be adopted". They also note that there is limited evidence that healthy individuals wearing masks in households or among contacts of sick patients, or as attendees of mass gathering may be beneficial, but that there is currently (emphasis added) no evidence that wearing a mask by health persons in the wider community setting is beneficial as a preventive measure.
They go on to say medical masks should be reserved for health care workers, as there is the risk of it being counter-productive (creating a false sense of security leading to a reduction in practice of other essential measures such as hand hygiene and distancing, along with increasing touching of the face), and where there are supply problems exacerbates problems with the supply to health care workers.
They also note that "In some countries masks are worn in accordance with local customs or in accordance with advice by national authorities in the context of COVID-19. In these situations, best practices should be followed about how to wear, remove, and dispose of them, and for hand hygiene after removal."
And they also say "The use of masks made of other materials (e.g., cotton fabric), also known as nonmedical masks, in the community setting has not been well evaluated. There is no current evidence to make a recommendation for or against their use in this setting."
Summarising that as "healthy people should not wear masks" is flat out wrong. The actual advice is rational, evidence-based, and nuanced.