This is what we use at work and its always the fix for Hades, Skull, Bean, and Box canyon NUCs. https://www.amazon.com/Accell-USB-C-HDMI-Adapter-Thunderbolt/dp/B01K9S0VYM/ref=sr_1_1?keywords=accell+U187B-005B&qid=1581836726&sr=8-1

Also when we have run out of USB ports we use this and retain a 1080p 60hz signal on top of adding devices. I know its not marketed as a thunderbolt3 but I've had no issues with the above NUC models. https://www.amazon.com/AUKEY-Charging-Multiport-Chromebook-Pixelbook/dp/B071ZPM6VQ/ref=sr_1_1?keywords=aukey+c59&qid=1581836875&sr=8-1

We typically drive 3x 1080p60hz feeds from skull canyons and 3x 4K30hz feeds from the Hades using these devices. This all done on top of Linux Ubuntu fwiw.

I bought this adapter that you have suggested: https://www.amazon.com/Accell-USB-C-HDMI-Adapter-Thunderbolt/dp/B01K9S0VYM/ref=sr_1_1?keywords=accell+U187B-005B&qid=1581836726&sr=8-1

The issue still remains with flickering/losing sync on the screen. As soon as I use the native HDMI port to HDMI on the monitor there are no issues.