The INUI power bank from JetBot is 5V⎓3A (dual output), so it works with Nano no problem. In the JetBot bill of materials, it lists quantity 1 of them, so only 1 is needed. What the JetBot notes are referring to regarding 2x is that it has 2 outputs, not that you need 2 of them. I’ve used this 10000mAh INUI battery quite a bit with Nano and not had problems with it.
If you want something bigger and with more capacity, check out this 25000mAh power bank, which has the added benefit of being able to power the Nano’s DC barrel jack in addition to USB.