Open Roblox and sign in
Go to Settings
Select Privacy or Parental Controls
Find Chat Settings
Set Who can chat with me? to No one
Set Who can message me? to No one
Disable in-experience chat if the option is available
For under-13 accounts, use the parental controls chat restrictions
On PC, you can also disable chat through Roblox website settings
On mobile, use the same account settings in the app or browser
Save the changes and restart Roblox if needed