This is why (just like for any other OS) you buy a device with explicit support. You don't buy a random laptop and then complain why macOS doesn't run on it... do you?
It's not exactly the same, though. You can buy a random laptop and throw Windows on it, even if it's not the version it shipped with. You can throw Linux on it, and it will almost certainly be usable; sound may not work, it may not resume from suspend, and graphics may be unaccelerated, but if will basically work.
If you're buying a new device, then yes, certainly you should shop for one that's supported on LineageOS or OmniROM, or whatever. But one of the uses of custom ROMs has been extending the life of older devices, and that ecosystem is very spotty.
"Sound may not work" and "but it will basically work" being in the same sentence is more-or-less why Linux is still not yet ready to take on Windows and OSX in the desktop space.
What you're describing is similar to the situation with mobile devices, only to a lesser degree. Turns out, making an OS run on hardware is challenging and under-appreciated work, and continuing to gloss over the complexity of it doesn't do solving the problem of open-source OSes any favors.
The problem you are describing is at once intractable and a solved problem. Most oems are at best ambivalent about Linux support. If you are lucky they provide enough documentation for volunteer labor to support their hardware otherwise someone has to for free spend their time reverse engineering their pile o' hacks.
Since there isn't an inexhaustible well of free labor to throw at other peoples hardware there will always be some hardware that either doesn't work right or doesn't work right out of the box because it requires fix foo that is only available in version bar that is the very latest that hasn't made its way into the stable version yet. If you run a bleeding edge distro you may find that you have the needed version of bar but they broke something else!
The solution is to buy hardware with the OS you intend to run in mind. If you are just curious about whether linux might be useful to you the easiest thing in the world to do is try it out either via live usb or virtual machine. If indeed you would like to run linux and it doesn't work with your existing hardware just buy with Linux in mind when you get your next machine.
Instead of asking whether linux can meet the impossible standard of running flawlessly on any pos you happen to throw at it ask whether there exists a reasonable range of hardware that meets your needs and expectations.
If you approach it that way you will most likely be satisfied.
That's basically my approach; when I want to run Linux (because the applications that run in Linux are useful for a wide range of things, and I'm very used to the command line), I tend to run it in a VM alongside / atop the Windows or OSX install that the hardware I'm using boots to.
The exception I regularly hit is raspberry pi, but in that specific case I (a) don't actually expect anything to really "just work" out of the box (the whole point of the platform is to hack around on it) and (b) I'm not trying to use it as my primary development / work / games / day-to-day environment.
If that sounds bad, then wait 'til you hear about Apple's situation - they don't support custom hardware, at all. Not only does sound not work, nothing works. Linux is a step above macOS in that it not only does it work very well when it ships with a computer, it also still works ok when you load it on any other computer. And yet, macOS has more users than linux does... Perhaps support on random computers is a bad metric for the readiness of an OS?
It is exactly the same. I put Windows 10 on an older Dell laptop. It mostly works, but it's not "supported" and I get blue-screens once in a while. There's just no practical way to keep supporting arbitrarily old devices, even for a company like Microsoft.
If it's exactly the same, I will hand you an unbranded phone with no OS and see if you can get Android running on it. The only machines you can't get Windows running on right now are Chromebooks, so 99% of personal computers will let you pretty easily install Windows in exactly the same fashion you would on any other computer. It might not run well, but it will certainly install. If it's exactly the same, do that with Android on any random phone.
Generic drivers have made explicit support mostly unnecessary in the desktop space. This doesn't exist on mobile. I've installed Linux effectively on many many pieces of junk whose designers never intended their hardware to be used that way.
