If you encounter issues while trying to use MetaMask on the Brave browser (such as an error saying Metamask is not installed, even though it is), you need to set MetaMask as your default web3 provider:
1. Go to Extensions Settings.
2. Change Web Provider for using Dapps to "MetaMask".
3. Restart the Brave browser.
If you're still having issues after following the above steps, reach out to support.