The same approach also works for the grid layout of an event.

Starting with Event Gallery 5.4.7, you can use the Breakpoint editor to add breakpoints to your site. This will generate CSS automatically.

Just add the necessary media queries and use the following CSS selector. The principle should be pretty clear and is easy to adapt to the tile layout.

.eventgallery-tiles-list .eventgallery-tile {
  width: 100%;
}