MacBook [Pro] - how many displays, what resolution/frequency? How do I find out the number, type, resolution &amp; refresh rate of additional monitors I can attach to my MacBook or MacBook Pro?

This is an attempt at a canonical QA, as per the Meta QA -
Where is the list of canonical questions stored for Ask Different?  to try prevent the myriad "same but different" questions we get on every possible combination of computers, cable &amp; monitors
There are perfectly good resources out there that Ask Different should not have to duplicate the efforts of.
This may not be the only available resource on this topic, but it is a comprehensive &amp; reliable one...

EveryMac, as the name suggests, has information on every Mac model ever made [also iPhones, iPads, iPods], including but not limited to the number of external displays supported &amp; their maximum specification.

If you are not absolutely certain which model you have from  Menu > About this Mac, then they have a search engine which can identify from many data types, serial number, part number etc, the  

Ultimate Mac Lookup  


  Lookup Macs, iPods, iPhones and iPads by Apple Order Number, Model Number, EMC Number, Model Identifier, Serial Number and Intel processor number.


This is an example of the data they provide for the current 2018 Core i9 15"



I have no affiliation to EveryMac, their partners, advertisers or sponsors.