Hi there,
The monitor that requires external power before connecting the Thunderbolt cable might have higher power consumption. The power delivered through the Thunderbolt 4 port on the Gti14 mini computer alone might not be sufficient to power up the monitor and transfer the video signal simultaneously. When you connect an external power source to the monitor first, it ensures that the monitor has enough power to operate properly and then the Thunderbolt cable can handle the data transfer for the image display.
When I tried our TYPE C monitor, it works without extra power, it has lower power requirement and can operate within the power limits provided by the Thunderbolt 4 port without the need for an additional power source.