Linux

thorough hardware certification process

Probably marketing speech for "an intern tested it once with the default setup and he reported there were no errors"

Broken standby on Linux

That is sometimes broken because of broken UEFI/ACPI implementations which the Windows drivers were made to respect and work around, but the Linux drivers who are often developed not by the hardware manufacture himself but rather 3rd parties who implement them according to the available docs/specifications, will then result in a semi-broken functionality because implementing something according to the specification doesn't mean much unfortunately if there are quirks or bugs you have to circumvent as well. This improves over time though with more adoption of Linux. When you compare the hardware support of Linux today vs. 20 years ago, it's become much, much better already due to more developers and users working on it / reporting issues, and also more and more hardware vendors becoming actually involved in the Linux driver development.

GPU bugs and screen flickering on Linux

Various hangs and crashed

Definitely not normal. But it's likely that it's just a small configuration or driver issue. Since you didn't provide any details, I just leave it as "easy to configure properly". I get that it would be cooler if it worked OOTB, but sometimes that isn't the case. It goes both ways, as well. It's hard to generalize based on few occurrences, but I also had problems long ago with a mainboard with its Realtek audio drivers on Windows which didn't work. Don't remember the details because it was long ago but I had to hunt for a very specific driver version from Realtek (wasn't easy to find), and couldn't use the one the mainboard vendor provided as the Realtek driver, nor the one provided by Windows by default. Anyway, of course Windows is generally better supported on most notebooks, I won't deny that, but that's simply due to market share, not because it's somehow made better. That's important to realize. If Linux had 80% market share, it would be the other way round, every manufacturer would absolutely ensure that their driver will work on all their distro targets and all their hardware models. In the Linux world, the drivers are sometimes made by 3rd party developers because otherwise there would be no driver at all, and so it's better to have a mostly functional driver than none at all. And that's also just because the vendors CAN ignore Linux based on marketshare. They shouldn't, but they can, and it makes short-term financial sense to do so, so it happens. Of course, if they market some of their models as explicitly Linux-friendly, they should absolutely ensure that such things will work OOTB. But even if they don't, it's usually not hard to make it work.

new laptops and Windows 11, basically anything works

Only because the manufacturer HAS to ensure that it works, while he DOESN'T HAVE to ensure that Linux will play nice with that hardware as well. I recommend using either notebooks from Linux-specific manufacturers (I had good experiences with Tuxedo for example) or you continue to use the "Linux-centric" notebook models from Dell/HP/... and then simply troubleshoot any shortcomings these might have. I don't know the model but it's very likely that it's a simple configuration issue. And I wouldn't recommend using the manufacturer's default OS. Especially not with Windows notebooks. Always reinstall a fresh, unmodified OS, and work from there. I'd even assume that if you leave out any vendor-specific software or kernel modules, your problems will probably vanish already.

I have effectively added €500 to my budget

That's an unfortunate reality also in other areas. Smaller vendors can't produce in mass quantities, and so they have to sell their stuff for more money, even though it seems counter-intuitive at first. But this is also the case with e.g. the Librem 5 mobile phone which is also very expensive (but a great option if you want a mainline Linux phone) [in this case, it's very expensive becaue you not only pay for the hardware, but also for the software development time], or well anything which isn't cheaply produced on a mass scale where you get volume discounts. So in a sense, if you want to change the status quo, you have to pay extra. So yes, buying a brand new Linux notebook isn't cheap, unless you want to specifically use an older notebook where Linux also happens to run on. But on the other hand, buying a pure Linux notebook also should generally ensure that it will work well. Similar to how when you buy hardware from Apple, they will ensure that OS X runs well on it.

I don't think that you can generalize anything from your or your friend's experience, so it seems likely that your friend misconfigured something or installed something the wrong way, leading to such stability problems. General tip: stability issues are almost always driver-related. Same as on Windows. So first try to remove all non-essential drivers (kernel modules on Linux) and see whether that improves stability. And, of course, check the logs. In most cases, they will point out the issue. I've also installed Linux on several "Windows-only" (not marketed as Linux compatible) notebooks and it ran just fine without ANY stability or graphics issues. I have a Lenovo ThinkPad for work and it runs Arch Linux, it's probably more stable than the Win11 it's supposed to run with. At least among my colleagues who run Win11 on it, I'm the only one who didn't yet have a driver or update issue within its lifespan. One of those colleagues even had to reinstall Win11 after a borked update. I also use Tuxedo notebooks (Linux-compatible by default) personally and they're great as well. But of course I never use vendor-supplied software, so I'm not affected if such software behaves badly. I always configure my systems the way I want them, starting from a vanilla base.