EDIT NOTE: This is a revised answer as my original answer was wrong!
It will not damage your RPi, but it won't work unless you use a
NON e-marked USB-C cable (details follow).
The Macbook Pro 87W USB-C Power Adapter has enough power to run the RPi 4B. The specifications printed on the adapter state that its 5.2 volt output is rated at 2.4 Amps.
HOWEVER..., it seems that the Raspberry Pi designers didn't read the USB-C specs, and didn't test their design very well before releasing it to production. This has been reported in several sources, including this post on TechRepublic, and further analyzed in this post by Tyler Ward. Or perhaps, The Foundation simply wanted to sell more of their "official" power supplies for the RPi 4B?
And so despite the fact that the Macbook Pro 87W USB-C Power Adapter (now replaced by the 96W supply) has more than ample power to handle the RPi 4, the RPi 4 is missing hardware that allows it to work with
e-marked USB-C cables. A design that is compliant with the USB-C specifications will work with
e-marked USB-C cables (more info); unfortunately, the Raspberry Pi 4 will not.
The reasons for this bodge are less important now than the remedies, so let's get on with that.
The (most practical) solutions are:
Buy the "Official" power supply sold by the Raspberry Organization, or
NON e-marked USB-C cable.
I saw no reason to cause the manufacture of yet another "wall wart" that may eventually wind up in a landfill when I've already got enough USB-C cables and chargers. It's a standard - right? And so I didn't buy the "official" power supply when I bought my RPi 4. For me personally, Option 1. is a "no-go" at this point.
For Option 2, Tom's Hardware has conveniently provided a list of USB-C cables they've tested that they claim will work with the RPi 4. Tom's also expressed understanding and compassion for the Raspberry Pi organization. I don't buy it, but to each his own.
I've not tried a different cable yet, but when I do, I'll follow up here with the results. In the meantime, I did try my Macbook Pro USB-C charging cable and 87W power supply. I confirmed that it DOES NOT power up the RPi 4. Also note that after trying my Macbook cable & charger on the RPi 4, I had to unplug and re-plug my power supply before it would charge my Macbook again! Just for grins, I also tried a new-ish USB-C charger made by Apple for an iPhone (18 watts as I read the low-contrast specs printed on the charger) with the same result: the 18 watt charger with Apple charging cable DOES NOT power up the RPi 4.
Follow up, 26 Dec 2019:
I obtained an el-cheapo USB-C charging cable (aka
NON e-marked cable) from Amazon. I tried this cable with my Macbook Pro 87W USB-C Power Adapter. This combination successfully powered the RPi 4B. I also tried this same cable with Apple's 18 watt iPhone charger. This combination also successfully powered the RPi 4B, and has continued to do so for more than 24 hours as of this writing.
Follow up, 14 Aug 2020:
Here's how to tell which version of the RPi4 you have (REF):
$ cat /proc/cpuinfo | grep Revision
If the result is :
Revision : b03111 It's an ORIGINAL RPi4 with USB-C design flaw, and a
NON e-marked cable is required for use with a USB-C charger.
Revision : c03112 It's a newer RPi4 with the corrective fix; you may use any cable - either an
e-marked cable, or a
NON e-marked cable.