If there is the slightest off chance that you use the iPad for gaming and want to hold on to it, go for the M1 one. Did you decide yet?
Yes I'll use the iPad to play lots of games. From YouTube reviews it seems that the Mini is capable on its own, even for intensive games like Genshin Impact (plus it's much more comfortable to hold on, like a Nintendo Switch). Most gaming reviews of the iPad Pro I've seen involve the use of controllers, suggesting that it's a bit heavy & cumbersome to hold for long gaming sessions.
On the other hand, M1 is more powerful and should theoretically last longer. There's talks about how M1 is currently too overpowered, but seeing how Apple is so focused on mobile gaming nowadays, we'll expect more GPU-intensive games in the future.
About reading: I'm a bit on the fence. Casual reading (i.e. ePUB files) is nicer on iPad Mini because its form factor is kind of like the Kindle. On the other hand, serious reading (academic textbooks) should be better on iPad Pro - PDF textbooks usually have 8.5" x 11" size so the 11" screen is better due to less zooming & more screen real estate for multitasking (reading & taking notes at the same time).
In a perfect world, I'd have 2 machines for 2 use cases. However, I have too many devices already (a desktop PC, a MBP, a work laptop, iPhone XS Max), and having 2 iPads don't make sense to me. I haven't finalized on my decision yet (the Mini has not arrived in our country yet) but I'm 90% positive I'll go with the Pro. There's also a minor point which helps sway in the way of the Pro: it has Silver color which matches with my MBP. It's a shame that Apple doesn't have that as an option for iPad Mini this year!