and after some reading couldn't exit it at all tapping both my back key and the back arrow on the top.
Due to how inconvenient the arrow on top is, I suggest to make it the exit button that closes the browser and returns user to Lemmy at once, while usual back buttons keep acting like they are now.
The back arrow does exit the browser for me, that link you posted it works fine with the back button and usually most links it does.
Every now and then a site will hi-jack the browser and that is when the back button won't work for me and you have to force close from within the three dot menu.
It hijacked internal browser for me just as you described. I proposed such change because I don't use this back arrow at all and it could've been handy as a force-close button.