You are using a standard USB power bank. It should be possible to power your project as long as you stay below the current limit (2.1A). Probably you should keep the intensity small enough to not exceed 1.9A in normal operation. That should be enough for about half intensity. You really don't want to exceed the current limit. And you should measure the actual current draw and then approach your own current limit (like 1.9A) from below. Calculations are good, but when operating like this you should look at the real values.
If you exceed the current limit of the power bank it depends on the implementation of the power bank what will happen. Most likely the power bank will cut the power but still work. Though it is also possible, that you fry some electronics inside the power bank and kill it this way.
- While you experiment with your code you can use fewer LEDs, so that they would be able to light up at full intensity. That makes sure, that you don't damage anything from a small programming error. If you write your code in the correct way (for example defining the number of LEDs at exactly one code line and reusing that name everywhere), then it will be easy to increase the number of LEDs to the target and also be sure, that you are staying within your limits.
- You already have it in your wiring diagram, but nonetheless I want to emphasize, that you must not power the LEDs through the Arduino. You need to connect them directly to the USB cable to the power bank. The Arduino cannot withstand such currents.
- USB power banks often cut power, when not enough current is being drawn from them (and for mine the current of an Arduino Nano wasn't enough to hold it active). If in your project the LEDs get turned of at some time, while the Arduino should keep running, the power bank might cut the power, thus turning off the Arduino. In my experience the bigger, more expensive power banks will do that, while small, cheap ones will just keep outputting the power. If this scenario is relevant for you, you need to test this yourself with your specific power bank.
If this battery will not be appropiate to this schema. What could I do?
You could use multiple of these power banks, each of them powering its own part of the LED strip. One of them can also power the Arduino. Just make sure to connect all grounds together.