I downloaded krita and started drawing. I tried to use the mirror tool on the toolbar and it didn't work. I uninstalled and reinstalled the program and it still doesn't work. Could it be a problem with my computer? I used the program on an old computer of mine but its not working with my new one. Any Idea of what is going on?

Works on my computer. I don't know what is wrong.
But if you can tell the process of how the tool is not working with screenshot or video of it, it will be a great help for someone

The quick burhs engine doesn't work with the mirror tool and there's a single preset that uses that engine, namely b)_Basic-1. Just use a different preset.