A lot of older disc-equipped hybrids used qr and mtb standards, because road disc standards hadn’t quite settled and there was a lack of parts, especially cheap ones. Works out fantastic- obviously the bikes are old now and don’t come up for sale that much but when they do they’re cheap, and you can hop them up with old mtb parts that absolutely nobody wants. Though it can be tricky to shop for them of course.
Mine is an old Boardman Comp which was an alright but fairly heavy bike when new, I added some skinny QR-only xc wheels that weigh 1500g, made it 1x, then added some narrow carbon bars, some old 9 speed X9 gearing and formula xc brakes that I had lying around. All just the stuff that nobody wants. I’m probably into it for about £400 all in, it’s super reliable and it absolutely flies, I genuinely wouldn’t change a single part of it and almost any newer flat bar bike would almost certainly be worse.