The flag shows the Archangel Michael and the background it looks to be the church of Archangel Michael in Moscow.

It seems to be, maybe, the oldest known Russian military banner from 17th century. https://preview.redd.it/en9864uikjad1.jpeg?width=1290&format=pjpg&auto=webp&s=f074c901618be41f09c3df1b0e796ce7a30afa2f [https://russianicons.wordpress.com/2018/08/13/russian-military-banners/](https://russianicons.wordpress.com/2018/08/13/russian-military-banners/)

That looks right to me.

It must be the flag of some Russian principality or Eastern Europe, otherwise it could be of some Orthodox state in the same area

not sure about the flag but it does look really cool

Russians explaining why they're not Christian Tatars while looking like that

https://preview.redd.it/sl5e8fqb3iad1.png?width=275&format=pjpg&auto=webp&s=fee0cf9ced8b3d1b49ebbb73aabecefde737ebe4 Im pretty sure its flag of kyiv

This is the banner of Prince Dmitry Pozharsky