QuickBooks Mac 20 are compatible with El Capitan.
QuickBooks for Mac may run on OS X 10.11 (El Capitan), but there are no versions of QuickBooks officially supported at this time. Apple’s new OS 10.11 El Capitan was released to the public on September 30, 2015.
Intuit has admitted that QuickBooks is not officially compatible with El Capitan even though users can still install it on OS X 10.11. My mid 2010 mac was working perfectly on El Capitan and though the Sierra upgrade went without a hitch the increased demand of the new OS caused my fan to go on overload just browsing static web pages. Of course, updating to the next version of Mac OS X will only be possible if the Mac hardware supports the new version. With an emphasis on performance and reliability, OS X El Capitan is expected to be a great system software update for Mac users.