Question about Einhell Quick start system CE-JS 18

This booster is not a power bank! For a power bank to be able to charge a notebook at all, it has to:
- support USB-C with Power Delivery (PD)
- deliver at least 30-100 watts, depending on the notebook
- have sufficient capacity (e.g. 20,000-30,000 mAh) to charge sensibly

This is normal.
This car booster is not designed for this.
Don't hesitate to Google how the thunderbolt works (usb-c on your PC) if you want to understand why it doesn't work.
As a solution, there are powerbanks specially designed for this (charging capacity > 65W).
I recommend the Anker brand (Anker Prime model).
Anker Prime (27650 mAh, 250 W, 99.54 Wh)