In the MacBook technical specifications documentation, I read that it supports up to 2 monitors (or 1, it depends on display parameters).
On Apple’s Thunderbolt 3 page, I read the same info but about a single Thunderbolt 3 port (of which I have 2).
What is the number of monitors I can connect to my MacBook Pro?
You can plug in a maximum of two monitors
The technical specifications gives you detailed info about what your specific model’s capabilities are. In this case, your model MacBook - 2017 13 inch MacBook Pro - has enough bandwidth to support two monitors at 4K or less or just one monitor at 5K.
The Thunderbolt information page gives you a generalized perspective of Thunderbolt’s capabilities.
According to the technical specification of your model:
Video Support
Simultaneously supports full native resolution on the built-in display at millions of colors and:
One display with 5120-by-2880 resolution at 60Hz at over a billion colors
Up to two displays with 4096-by-2304 resolution at 60Hz at millions of colors
Up to two displays with 3840-by-2160 resolution at 60Hz at over a billion colors
Thunderbolt 3 digital video output
- Native DisplayPort output over USB‑C
- VGA, HDMI, DVI, and Thunderbolt 2 output supported using adapters (sold separately)
therefore you can have 3 active screens including the screen of your MacBook.
The 2 connected monitor can have a resolution up to 4K.
If you wish to connect a monitor with higher resolution than 4K (e.g. 5K), you will be able to connect only 1 additional monitor (i.e. 2 active screen configuration).
In general, to be able to connect even more monitors you need to have a dedicated GPU. A similar question was addressed here.
I have tried plugging in an Apple thunderbolt display using Apple's own USB-C to thunderbolt adapter (purchased from the apple store) - works great. - I can also connect a Dell 1080p, USB-C monitor -- but not both at the same time. - I am considering trying with a diff monitor.
