We have the Bolsheviks to thank for it! (E: to be clear, and as will be evident by the links I shared, I am not a Leninist lol)

My summation of the concept is obviously superficial, here are some good places to start getting a better idea of what it is and where we might start:

https://www.weareplanc.org/modules/wtf-is-dual-power/

https://medium.com/@anarchist.environmentalist/an-anarchist-dual-power-e911edf66ad7

https://blog.pmpress.org/2019/09/02/alternative-institutions-or-dual-power/

https://theanarchistlibrary.org/library/petr-kropotkin-mutual-aid-a-factor-of-evolution

https://theanarchistlibrary.org/library/the-anarchist-faq-editorial-collective-an-anarchist-faq-full (there isn't a specific dual power bullet point, but it does come up, and in general this document is worth looking through)