The Material Theme revamp is rolling out to some Google Maps users, though this seems to be a server side switch that Google has to toggle on and not an update which brings in the new visual changes. Judging from the screenshots below it looks like the users who have this new design in Maps are located in different regions, so it's not clear if Google is rolling out the new design only in certain locations or just on a smaller scale at the moment. Either way, it appears that some users are getting the new look which possibly means that more and more users will have the design change in due time and it's likely just a waiting game at this point.
While some Material Theme changes have been hitting Maps for weeks or more, those were a select few changes and this new design revamp of sorts is adding the new look to pretty much every corner of the application. The Search bar up top for example has a new, more rounded look at the corners, as do any of the things in the app that used to have a more squared off shape, such as image thumbnails for the galleries of places.
If you have the new design of the interface, "search nearby" is now "explore nearby" and has a few categories of locations you can search or browse through listed at the top, which includes restaurants, coffee, and attractions, and then the fourth button is the more button for exploring other types of categories beyond the ones that are listed before it. With the new look rolling out to some users at this point it's possible that many users may see the visual design change by the end of the week. If you don't use Maps much it's also possible that you may not have noticed the design changes already taking place, keeping in mind that this isn't focused on requiring an update.