A common mistake when installing Procreate brushes is attempting to import your downloaded files into Procreate directly from the Procreate gallery's import button. This will result in your brush files being greyed-out when importing.
Your downloaded brush files can only be imported via the following path:
Files app > iCloud Drive > Downloads > tap the Procreate brushset file to install.
Files app > on my iPad > Downloads > tap the Procreate brushset file to install.