Flow does support screen mirroring. Alas, I can only confirm this on Windows PCs. Don't see why they wouldn't support the feature on a Mac, but stranger things have happened.
unfortunately with all my searching it looks like Samsung has decided to leave Apple (Mac) users out altogether with their Flow app. Major disappointment as Samsung's SideSync worked great with Mac and still does! Grab that if you don't have it as next month they stop support and take down the apps for PC & phone. Makes no sense other than their relationship with Microsoft... Good luck!
VNC would still work - server on the phone, client on the Mac. It's not vendor or PC dependent. There are both servers and clients for both Android and Mac.