I searched and found this link:
I think it's your charger/power bank. As you can see on the description on the device and the link, the output is
2.1A (2.1 Amper) at
5V (5 Volt DC).
On the other hand, "The Foundation's" published figures for power consumption across all models of Raspberry Pi shows a figure for RPi 4B which is 3.0A at 5V.
All in all, your charger/power bank may turn on the Raspberry Pi 4B but it's not safe, at all.
As stated in the Raspberry Pi Model B specifications found here, the "minimum*" current for the Raspberry Pi 4 via the USB-C connector and GPIO headers is 3A. (* being a "good quality 2.5A power supply can be used if downstream USB peripherals consume less than 500mA in total.")
Also, in the answer to this question, the user states that while 3A is "recommended", 2.5A is the "minimum".
These values are well above the 2.1A output stated on the charger that you have shown us. Most likely, the charger will not work, and the Pi will either lose power the second after it starts booting, or lose power under intense loads on the CPU. Also, from personal experience with my Pi3 B+, I found a 2.1A charger doesn't work at all.