My MacBook won't airdrop with iPhone 8

You didn't state what MacBook model you have, only the OS X version. You need a 2012 or later Mac model to communicate with iOS devices for AirDrop...

From Use AirDrop to send content from your Mac - Apple Support

AirDrop system requirements

To send items to an iPhone, iPad, or iPod touch, or to receive items from those devices, you need a 2012 or later Mac model with OS X Yosemite or later, excluding the Mac Pro (Mid 2012).

To send items to another Mac, you need:

• MacBook Pro (Late 2008) or later, excluding the MacBook Pro (17-inch, Late 2008)
• MacBook Air (Late 2010) or later
• MacBook (Late 2008) or later, excluding the white MacBook (Late 2008)
• iMac (Early 2009) or later
• Mac Mini (Mid 2010) or later
• Mac Pro (Early 2009 with AirPort Extreme card, or Mid 2010)

Follow my link above and follow the steps to (re)setup AirDrop between the desired devices.

Also see Use AirDrop on your iPhone, iPad, or iPod touch - Apple Support

*This is a different link than the one posted above

I have the same problem, I took it to genius bar and also seek help from Apple staff online, but still couldn't fix the problem permanently. When I signed out of iCloud and signed back in, I was able to temporarily airdrop, but doing this everytime would be super annoying. I hope Apple can come up with some way to fix this compatibility issue.