The search engine is keen to ensure its users have a good experience. It doesn’t want to show search results on mobiles for web pages that will be hard to read on a phone. It wants to prioritise things that will be useful.
So, if your website doesn’t pass the mobile-friendly test, you may find it hard to achieve visibility in search results, which will impact the traffic your site attains.
What Google is looking for is quality pages that are relevant to searcher intent. It wants to present results that match what people are looking for. If a searcher sees your website in the results and clicks through, this is a signal to Google that your result was at least enough to attract a click. But if the user clicks back to Google within a couple of seconds, this could tell Google that they didn’t like what they saw,