How is work built from the computing subsystem of the device in a cross-platform environment?

Do you need native products for this, how big is their presence?

Most of the basic needs of a developer are already covered by the capabilities of cross-platform tools. But everything, as they say, depends on the context. If we are talking about some complex animations, working with video, camera processing, then it is better to turn to the native part of the environment.

Do you need elements of native development in all cases of working with the computing subsystem of a smartphone? If not, please provide examples where such interaction is provided by framework libraries (for example, React Native or Flutter)

Usually, these frameworks do a good job of covering the needs of a developer in terms of screen layout, basic networking, in general, everything that is needed for an ordinary application. On the other hand, navigation patterns are well implemented in them, which is neglected by many inexperienced native developers or was neglected earlier, even at the very dawn of mobile development, now the entry threshold has become higher and it will be difficult for a person without these skills to survive in the market.

Is it possible to compare the performance of native products with the performance of cross-platform ones?

Personally, I would not, because. decided everything for myself. But it is always possible and necessary to compare, and this is where the truth lies. A tool like Component Kit, the progenitor of React Native, once showed us what high performance is like compared to regular native tools. But that was just a Facebook case that spawned both of these technologies. Most of the others are still unoptimized, and it's hard to say how they will behave in the case of your application.

If cross-platform frameworks have lower performance than native languages, how noticeable will this be to the user?

As I said above, for the average user it will be rather imperceptible. But this is only if the developer was extremely careful, knew what he was doing, did it not for the first time, and was familiar with most of the problems of the technology that he was using. But in the general mass, it must be admitted, given the low threshold for entering the technology for developers, such applications will be very visually different due to the lack of smooth animations, visual components that are not native to the platform, and also have poor layout on some rare devices.