Russian Orthodox churches actually draw the same inspiration as most mosques. Roman church architecture started with this as inspiration:
https://en.wikipedia.org/wiki/Pantheon,_RomeA famous example of the development is the Hagia Sophia: https://en.wikipedia.org/wiki/Hagia_Sophia
There's many examples of Byzantine era architecture which were the inspiration for Islamic mosques (many actually being converted into mosques):
https://en.wikipedia.org/wiki/Byzantine_architecture
Now, if you know the history of the Russian Orthodox Church, or rather how Slavs became Orthodox in the first place, you'd know it's because the first Rus kingdom made contact with Byzantine Greeks and converted to Orthodoxy, hence the Greek influence in Russian (indeed all Slavic) churches.
Anyhow, the specific architectural style of the Cathedral of Christ the Saviour dates back to the 11th century: https://en.wikipedia.org/wiki/Russian_church_architecture
The inspiration of the Cathedral of Christ the Saviour was also said to be the Hagia Sophia, although IMO it looks more like early Russian cathedrals. Also, not sure about the angle you chose, but Christ the Saviour looks quite different from the Taj Mahal: https://en.wikipedia.org/wiki/Cathedral_of_Christ_the_Saviou...
Both do draw from the same architectural tradition, but the Taj Mahal's inspiration goes like this:
Pantheon/Roman Architecture -> Hagia Sophia/Byzantine architecture -> Islamic invasions -> Persian Architecture -> Mughal Architecture
Whereas Russian Church designs came from the same initial source but diverged in the 11th century:
Pantheon/Roman Architecture -> Hagia Sophia/Byzantine architecture -> Rus Empire conversion -> Russian Church architecture.
If anything, Russian churches do draw a bit of inspiration from western church architecture of the Renaissance (there's a well-know period of time where the Tsars attempted to westernise Russia), see St. Peter's Basilica: https://en.wikipedia.org/wiki/St._Peter%27s_Basilica#/media/...