Despite predating Minecraft by at least a few years, Roblox didn't reach its current levels of popularity until the late 2010s. You could argue that it's one of the games that benefited a lot from the pandemic, similar to Fall Guys, which, by the way, is going free-to-play.
Having said that, Roblox is available on a lot of devices. Unfortunately, it's currently not on the Nintendo Switch.
At the moment, players can only download and play Roblox on Windows PCs, Mac, iOS as well as Android devices, and Xbox consoles. The Nintendo Switch, as well as both PS4 and the PS5, do not support Roblox.
Make no mistake, Roblox is not an Xbox exclusive. At least, as far as the public is concerned. The accepted explanation is that Roblox uses a massive amount of external assets because it is a game that can be best described as "Minecraft on steroids." However, unlike similar titles like Minecraft and Fortnite, Roblox allows players to use assets from external sources. Depending on who you believe, it was either the Roblox team's inability or their outright refusal to filter out the said assets that ultimately doomed a PlayStation or Switch port of the game.