The mouse cursor can go off screen on Roblox if you have set the monitor scaling above the recommended limit. By default, the limit is set to 100% (depending on the display resolution).

An alternative bootstrapper for Roblox with a bunch of extra features. - Adding custom mods · bloxstraplabs/bloxstrap Wiki. ... Mouse cursors - located in content\textures\Cursors\KeyboardMouse\ - ...