I think Morbius' statement may have been speaking to the notion that we can have The Ultimate (something) that does everything well, and I've found that to not be the case, especially with bicycles, which are basic enough so that they're generally optimal at only a few things. A bike that excels on mountain trails won't be best on the road. And vice versa.

In your case, I think any bike with a light frame and clearance for large tires will work. Do you ride in the rain and want fenders? That may somewhat limit your choices. Do you tour and/or carry racks/bags? That may somewhat limit your choices. When you start to consider all the things you do on a bike, you may come back around to the desire to have more than one. But, if your use case is pretty narrow or focused, then you can probably manage with one bike. Note also that this is a forum for bike enthusiasts, so we're already pre-biased towards "nicer" and/or "more". Of course, most of the world gets by on bikes we would buy at Walmart, and they go places that we wouldn't, so our perspective is already different than most.

Consider a fat bike with street tires. My dad just got a Surly Pugsley and put Origin8 Supercell tires on it (street tires) and it's a real riot. Consider a steel framed flat bar bike like a Surly Troll. Consider an older used bike like a Trek MultiTrack -- they have steel frames and clearance for wide tires. My 1997 MultiTrack 750 works great as a light "mountain bike" with 40mm tires. I found that I wanted to do more than that bike would do (or I just didn't want to beat it up), so I bought a dedicated 27.5" mountain bike. You don't have to spend a lot of money. I paid $155 for mine and have a total of about $350 in it now including better drivetrain, hydraulic disc brakes, very nice Vittoria Mezcal tires, etc.

Of course, you can find a bike that "can work" on nearly all surfaces. A street-tired fat bike and/or something like a Troll is probably the most "all-rounded" bike type you can find. All types represent compromises, though, and you just have to determine which ones you are willing to accept.