Does travel insurance covers hiking on high altitudes are participation in shamanic ceremonies?

For (1), back when I was shopping around for insurance for a long trip which included a high-altitude trek in Nepal, most plans had some sort of altitude restriction in the fine print (though I don't remember what it typically was), or sometimes a very aggressive definition of "mountaineering". If I remember correctly some of them even offered an extra paid option to ease the restrictions. But I did manage to find a plan without such restrictions (it was Cigna, no idea whether their plan details are still the same). But short-trip plans may be less restrictive, I was only looking at long-term plans (i.e. travelling around a year).

As for (2), I don't know for sure, but I'm guessing you can find a plan that would only exclude illegal drugs. So if you manage to find such a plan, if the substance you're consuming is legal where you're consuming it, I don't think you should have a problem. But this is just my guess, I haven't actually tried finding such plans myself.

It would be nice to know where to find insurance that would cover scenarios like 1) and 2)

It's not a “generic” travel insurance but alpine clubs (e.g. the German Alpine club or Austrian Alpine club) offer insurance covering rescue and medical costs resulting from mountaineering accidents as part of their regular membership. The exact conditions differ a little but both also offer extra travel or “expedition” insurance for things not included in their regular insurance cover (mountaineering above 6000 or 7000 m, hard-to-reach areas like polar regions or Greenland, generic travel insurance, long-term travel).

For the DAV (German Alpine club), package tours abroad seem to be excluded but I see no similar restriction for ÖAV and they have some info in English and a “Britannia” chapter so I would look at the latter first (usually you would become a member of the chapter or Sektion for your locale and only incidentally of the national organization but I think it's also possible to become a member of the Austrian club directly). Membership fees are around €60-80, I don't know how this compares to the insurance products you were considering.

(I mentioned the clubs from German-speaking areas because the venerable British Alpine Club apparently does not offer insurance of any kind.)