While there's not a Roblox app for ChromeOS, it's still possible to play using the Android app on some Chromebooks, or by streaming the game.

Once downloaded, here is how you can play any game on the platform: On your Chromebook, open the Roblox desktop application.

As the access is denied and players can’t open Google Play Store through their school Chromebook, unfortunately, they can’t play any Roblox games on the Chromebook.