Google said even though Chrome 41, how GoogleBot sees the web, doesn't support CSS Grid Layouts, Google is still able to index the content on those pages. John Mueller of Google said on Twitter that even though the layout might break, the content is still there and Googlebot can index the content find.
CSS Grid Layout excels at dividing a page into major regions, or defining the relationship in terms of size, position, and layer, between parts of a control built from HTML primitives.
Like tables, grid layout enables an author to align elements into columns and rows. However, many more layouts are either possible or easier with CSS grid than they were with tables. For example, a grid container's child elements could position themselves so they actually overlap and layer, similar to CSS positioned elements.
You can learn more about this on the Mozilla developer center.
Here are the relevant tweets around this:
If we can still reach the content, we'll still be able to index it. If it just breaks the layout, that's fine.
— John ☆.o(≧▽≦)o.☆ (@JohnMu) April 5, 2018
Forum discussion at Twitter.
Note: I am currently offline for Passover, this post was prewritten and scheduled to go live today.