Greetings. My name is Anis. I'll be glad to help you today.
It appears that there are some residual files left even after uninstalling Roblox.
Please run Disk Cleanup and remove unwanted residual files and clean up some storage space.
Type Disk Cleanup at the Start Menu, click on it when it appears.
Select C: drive and click OK
Now click on all the check boxes and press OK.
Wait for the process to complete.
Now, press Windows+R together to open Run box.
Enter the following command and press Enter.
%localappdata%
It will take you to a directory. Find Roblox in this directory.
If you find it, simply delete it. If you do not find it, that means Roblox is completely removed.
Let me know how it goes?