DP to USB-C does not provide power.

Did you connect any kind of power source to the portable monitor?

Yes I do with another USB C to power source (of course, not from the PC)

all I get is “no signal” on the screen

Is it this one?
https://www.viewsonic.com/global/products/lcd/VX1655-4K-OLED#specs
Does it work with the mini HDMI to HDMI cable?

Does the PC recognize any additional displays?

Yes.
Mini HDMI is the only port I am using right now.
The portable monitor has 1 mini hdmi and 2 USB C.
Only mini HDMI work as intended. The USB C only work as power supply ports.
I want to use USB C as mini HDMI

Have you tried the joy stick on the back of the display to adjust input?

From the Manual, have you followed these steps?

Power Delivery – Further Information
Due to the VX1655-4K-OLED’s design please note:
•
The first connected device will be the main input signal.
•
When a Type C port recognizes an external device as a power adapter, it will only distribute the power. It will NOT display the input signal.
•
Only when one of the Type C ports is recognized as a power adapter can the other one deliver two-way power.
If a laptop is connected first to the VX1655-4K-OLED, then a mobile phone is connected second, the mobile phone’s battery will not be charged as neither Type C port recognizes the connection as being connected to a power adapter.
NOTE: If you want to display the mobile phone’s screen, you must unplug the Type C cable connected to the laptop.
If a mobile phone is connected first to the VX1655-4K-OLED, then a laptop is connected second, the mobile phone’s battery will be charged as one of the Type C ports is recognized as being connected to a power adapter.
NOTE: If you want to display the laptop screen, you must unplug the Type C cable connected to the mobile phone.
Due to the VX1655-4K-OLED’s design, do not connect two laptops or one laptop and a desktop computer at the same time. This can cause power distribution conflicts, resulting in flashing screens or the forced shutdown of the laptop(s).
NOTE:
•
If the laptop has a Type C port, please connect via Type C to the VX1655-4K-OLED.
•
Do not connect the other Type C port of the VX1655-4K-OLED to another laptop or desktop computer via Type A and HDMI at the same time.
•
If the laptop only has HDMI and Type A ports, please connect via HDMI and Type A to Type C to the VX1655-4K-OLED.
•
If the power output of the Type A port of the laptop is not greater than 20W, please use our power adapter to connect to the VX1655-4K-OLED.
•
Do not connect the other Type C port of the VX1655-4K-OLED to another laptop or desktop computer at the same time.

My assumption is that de monitor does something “weird” when connecting both USB-Cs. Can’t put my finger on it tho.
Highly doubt the cable is at fault.

Amazon Basics cable actually works and just 60% the price of 3D club cable!

Gonna return 3D club cable