The NUC8i3BEH product spec page claims this model can support 3 displays, however the compatibility page only lists single output thunderbolt dongles. What dual display output thunderbolt adapter will work for this model for a 3 monitor setup?
The USB-C connector offers two ways that multiple monitors can be connected, via the embedded DP interface and via the embedded TBT3 interface. Two (or even three) monitors can be connected using a MST Hub. The issue with this method is that the connected monitors must share the bandwidth of the DP interface. While two 1080p (or 2K) monitors can be supported at 60Hz, two 2160p/4K monitors can only be supported at 30Hz. If the TBT3 interface is used instead, the throughput capability is almost doubled and two 2160p/4K monitors can be supported at 60Hz.
These can support two 2160p/4K monitors at 30Hz:
MST Hub adapter supporting two HDMI monitors: https://www.amazon.com/USB-C-HDMI-Adapter-Thunderbolt-Compatible/dp/B06XPVGQKY.
MST Hub adapter supporting two DP monitors: https://www.amazon.com/USB-C-HDMI-Adapter-Thunderbolt-Compatible/dp/B01KIMP28Y?th=1.
These can support two 2160p/4K monitors at 60Hz:
TBT3 adapter supporting two HDMI monitors: https://www.amazon.com/Cable-Matters-Thunderbolt-Supporting-Compatible/dp/B01DYFI0AY.
TBT3 adapter supporting two DP monitors: https://www.amazon.com/Cable-Matters-Thunderbolt-DisplayPort-Supporting/dp/B01DYFI1OE.
For native TBT monitors, daisy-chaining can be used to connect two monitors to the USB-C port.
Another alternative is the use of a hub, such as this: https://www.amazon.com/Belkin-Thunderbolt-Transfer-Compatible-F4U085tt/dp/B00NAWCU7G.
Hope this helps,