Google uses mobile-first indexing, which means the mobile version of your site is the one Google prioritizes when evaluating rankings. If your site does not work well on mobile devices, rankings drop, regardless of how the desktop version performs.
Beyond the ranking impact, the mobile user experience is critical: more than 60% of web traffic in Brazil comes from mobile devices. If visitors have to zoom in, scroll horizontally, or fight with tiny buttons, they leave. That increases bounce rate, which is a negative signal for Google.
Responsiveness goes beyond "the site fits on the screen". It includes: text that is readable without zooming, buttons and links with adequate touch targets, forms that work on small screens, images that adapt to the screen size, and accessible navigation menus. Test your site with the Google Mobile-Friendly Test and with Chrome DevTools using device emulation.