CSS Grid Garden
CSS Grid Garden is a fun simple game where you use CSS grid properties to water carrots in a garden and kill weeds. The carrots and weeds change location each level and the user has to select the correct grid property to water each plant or poison the weeds. This game also appears to be made by the same person that created Flexbox Froggy based on the style of the game and the referral link at the bottom of the page.
Coding Fantasy - CSS Grid Attack
CSS Grid Attack is a game where elves are chasing after an evil elf to rescue another elf with their powerful weapon - CSS Grid. In the game, you use grid properties to help the elves on their journey by leaving monsters in red zones and keeping your character in the green zones.
Learn CSS Grid
Learn CSS Grid is a one-page guide to learning how to use CSS Grid. This resource is not very interactive, but it is laid out well with simple visuals walking the user through each grid property.
Summary
Overall, there are lots of resources online that can be accessed for free to learn CSS grid. Many of them are games which can help users learn coding better. Out of the three resources above, I recommend using CSS Grid Garden to learn grid because of how simple, fun, and straightforward it is just like Flexbox Froggy.