There is currently no way to officially download and play "Roblox" on the Switch, and Roblox Corporation hasn't made any solid statement on whether or not it will be in the future.

Roblox How to download and when can you play Roblox on PS5, PS4 and Nintendo Switch? Roblox is coming soon to new platforms like the PS4 and PS5, opening up its creation tools and community for ...