Won't get 5v on input of Arduino with power bank
The big component marked 2R2 is an inductor. That's a tell tale sign of a boost (or buck) converter. This allows the power bank to output higher voltage (or more current in case of a buckconverter) than the batteries are able to provide.

Boost converters work by shorting the inductor to ground and then using the stored energy to boost the voltage.

Most power banks using such a boost circuit will have a sensing circuit to turn it off if there is no load.

The simplest method of keeping the circuit enabled is by adding more load to increase the current.