On most big modern smartphones the screen is simply too tall to reach the top of it with the fingers from your main hand that’s holding the phone. So you hold it with your left hand, possibly type with two thumbs and to reach the buttons at the top (e.g. the oft use back button on Grindr) you have no choice but to use your right hand and physically move it to the top of the screen to use these buttons. You cannot use Grindr with one hand only. Most apps are like this but please have a look at the Flipboard app. It’s designed for one handed use with all the home, back and forward buttons at the bottom. (See two screenshots attached). This is also why Apple moved the Safari search bar from the top to the bottom. (See third attached screenshot).

So please consider how Grindr can be updated to be operated by only using one hand and having all the control buttons, and specifically the Back button, at the bottom.