The real "problem" is how you make it work without a monopoly system like Google's or Apple's or Steam or Microsoft. They have to varying extents made monopolies where app makers want to list in their store, and accept they take 30% of the revenue because they are the sole gatekeeper to a large number of users. That model doesn't work in Linux because you can't create a monopoly to force someone to use your store.
Microsoft keeps trying in Windows via sheer scale but UWA's are not a monopoly so people currently largely bypass it. Microsoft even now lets App makers keep every penny of money generated "in-app" (except for games) as it's desperate to try and grow. Canonical has tried it with Linux and has also failed because ultimately it isn't a monopoly and it's method of Debs as the article said didn't really work. Steam works cross platform because of sheer size and it's managed to make a convenient cross platform library which gradually locks users in to an extent, and also forces publishers to list it's game there. It's very difficult to get to that kind of scale to be compelling.
For an "App store" to work in Linux under the currently "accepted" business model, you'd need to find some way of making it a monopoly or compelling somehow so that users will buy in and the 30% price tag to App makers becomes impossible to ignore due to the scale. I can't see that happening. Google did it with Android by forking Linux and making it an entirely walled garden it controlled; the free route into that garden is there but is very marginal and you have to bypass security measures to get to it.
The only way I can see it working in a limited fashion in Linux is if someone makes an "at cost" model where the share of revenue taken by the app store is purely to maintain the store (including the payment system, any "drm" that might be needed etc). That sounds like the Flathub route. But I can't see it growing rapidly or being compelling for App makers to take a risk on - it'll probably take a long time to gradually grow and prove itself as a reliable way of monetising apps.
Whether or not we need monetised Apps in linux is a whole other question. For me personally, aside from Games, all the software I use on Windows and Linux is free OR a subscription service (such as Office paid for by work, or my Email, Password manager and Backup software which I pay for). On my phone, the only software I've ever bought has been low level - like a music player or a theme app; and that has been an engineered demand because Google has a monopoly, which largely keeps out the opensource community allowing app makers to step in. I bypass that now with F-droid. I accept I'm part of the exception in Android, but most users have that expectation in Linux and Windows.
I don't see a substantial "app store" type eco-system growing in those environments. If someone is willing to give it away for free as FOSS, then it leaves little room for App makers for low level software. The only route to make money is then the "premium" or value added models, and a lot of that is going subscription model - software as a service. App stores are largely the result of closed eco-systems; in an open eco-system like Linux and even Windows it just doesn't make much sense.