Is it necessary to click on the ad? Or is it enough to go to the web page where the ad is displayed?

Why is Kiwi a terrible browser?

In settings there is "open links in apps". If you change this links are indeed open in the default browser

It indeed works, but Firefox and derivatives are really slow on my phone :x

Why do I need a NAT rule if the computer uses DHCP?

With an old phone Firefox is indeed slow. Startup is slow, page loading is slow, even scrolling is sluggish. On Chromium browser the performance is a lot better if your phone is not that fast.

Makes sense, is their any downside if I set the same DNS in Android and Router?

On Firefox it works if you change the settings, but unfortunately i don't know any Chromium browser with that feature.

But Kiwi doesn't open links from PWAs in default Browser, so no solution for me