Does anyone know how I can convert/open an
sbrz file on my Mac? Hoping to turn it into a PDF.
According to the FileSuffix.com website, this suffix is for the "Sky Ebook Reader Encrypted Ebook". Because the file is encrypted, it is not (generally) legal under DMCA to remove the encryption (in the US). And of course, as you certainly have already found, the Sky eBook Reader company only offers their software on Window.
The format is not used by any of the major ebook companies, as far as I've been able to determine. There is a message on the MobileRead forum from the developer of the Calibre program that he has no plans to support that format. While a solution might be available eventually, it does not appear that one exists at this time.