“or in any way becomes legally available to a significant portion” if this is your definition. Then Naltrexone should resolve to yes.

Hmm yes, that's not the intention of this question, because it's off-label and already available. (Technically, other medications like triple anticoagulants can also be prescribed off-label)

I will change it to: 'or in any way receives an indication for' a significant portion of Long Covid and/or ME/CFS patients.

Would mayo clinic proceedings having it in the list of ME/CFS meds count. Or for the US, only FDA approval counts?

Only FDA approval