I don't have a source for numbers, but I've read a handful headlines about tech companies building nuclear reactors for their datacenters.
Flip
What incredibly enough hasn't been brought up yet, is the distinction between gender preference and genital preference. In heteronormativity they're assumed to be the same, but in reality they're not. This way of thinking also lends itself to the flexibility you're describing; note the word "preference".
Paywalled, but even the bit I could read I don't agree with. It works great where I live, and totally does cut down on lines! The supermarkets I go to usually have one manned line, and 6-8 self-checkout terminals manned by a single employee. In one discount store the person manning the normal line also has the self-checkout, unless someone else is nearby, and that isn't ideal. But even then, I get to stroll past people who can't figure the system out, and maniacs who are either paying with coins or arguing over lettuce prices.
It works fine 80-90% of the time, and the employees are pretty swift to help, because it's usually one of two problems: Either I'm buying alcohol, or fruit and veg that's in season doesn't have uniform weight. Otherwise it works great.
The one grocery store I regularly visit that doesn't have it is a nuisance, because I wait in line every time.
Seconding Obsidian - it's not FOSS, but the files are just markdown, nothing special, so you're not locked in. Self hosting is real easy, you just have to Sync the files, and everything follows. I use syncthing between my laptop and phone and am having a good time with it.
Not to say that they're somehow clean, more so that the energy demand is insane enough to warrant considerations like this