I'll only speak to Europe. Pretty much every flight in Europe has some % chance of being assigned a hard stand, so you can never eliminate the possibility of having to use stairs entirely - this includes long-haul wide-body flights at the likes of LHR. However, if you tick the box saying you require assistance when you buy your ticket, they should board you using a lift like . Some airports (LGW for example) have introduced zig-zag ramps like this to make life easier for those who find steps difficult (I think these are the ones mentioned above as appearing in the US).

In general, both LCC-heavy and highly-seasonal airports are more likely to have you board by stairs, and LCCs are less likely to use jetbridges than non-LCCs. Legacy (subsidiary) flights operated by planes with fewer than 6 seats across are more likely to board by stairs. Even where a plane is hooked up to a jet bridge, some airlines will board people in the rear-half of the plane by stairs to expedite boarding - Easyjet even tells you whether you ought to board from the Front or Rear on the (mobile) boarding pass. It's not just LCCs though: LCY is just about the furthest from an LCC/seasonal airport, and it has no jetbridges because there's simply no space for them.

I don't think I've been spared a non-jetbridge boarding/disembarking at any European airport I've visited 5+ times, it's very much a part of flying life.