Bloxstrap cannot download Roblox
This problem happens when Bloxstrap is trying to download the files for the Roblox game client. However, there’s an unknown rare Windows bug that causes downloads of large files to be corrupted. So this isn’t actually a problem with Bloxstrap, and it happens with Roblox’s official launcher too.
The most common fix for it is to just restart your computer, and then try and launch Roblox again. If you’re still having problems, it’ll probably just fix itself at some point. Otherwise, you’ll just have to stick to the original Roblox launcher (if it even works).
If nothing else works, unfortunately there’s not much else yo can do. Please do not open an issue for this.