Let me guess, you "need" a more sophisticated UI toolkit on mobile? ;-p
With Qt Widgets you'll have to go out of your way to make it work nice with touch devices, since it has been created for desktop usage with mouse and keyboard input in mind, while Qt Quick has been made with mobile user interfaces in mind.
I wonder why you're worried about the performance of Qt Quick. It has hardware rendering by default and the layout system is designed with applications in mind, unlike HTML, which tries to retrofit a document markup language into an application markup language. Additionally, QML and JavaScript files can be precompile to native code, if the JIT compilation of QML and JavaScript files would be a performance concern.
QML just sits in this sweet spot of being easy to use for developers while not consuming too much ( Electron-levels) of system resources. Of course, if you abuse QML you can most definitely create slow applications in it, but you could say that about every framework.
I basically use cash wherever possible, otherwise by debit card, iDeal (almost all Dutch webshops accept it), SEPA and as a last resort PayPal, even though I despise that company.
I feel bad for everyone who has to use credit cards. While you do get cashback, some form of insurance and possible some rewards for using them, you as a consumer basically have to pay for it due to stores increasing prices due to the high transaction costs (I believe about 3% of the transaction, but It'll likely be different for everything else).
Compare that to the Netherlands, where as far as I'm aware, stores have for debit cards a flat transaction fee of about €0,15 per transaction and a monthly fee. Although that obviously differs from payment provider to payment providers, a store for which I work has a monthly fee plus one for closing a shift.
Anyways, due to the cheaper costs of accepting debit cards almost every store accepts them, while credit cards mostly aren't accepted in physical stores. It seems like most Dutch web shops do accept them, but most people here don't have credit cards at all. I assume they are mainly for people who buy outside of the Netherlands.
This is also the reason why I have PayPal. It sucks, but it sucks less for me than a credit card and is widely accepted.