Did Gen5 ever answer what happened? Cause I have a head cannon

The first movie starts off with a really interesting plot: magic is literally gone, the 3 pony types hate one another, and its in modern times. Twilight sealed the magic in 3 crystals before disappearing due to an unknown threat... but what if Twilight WAS the threat?

Twilight is the element of magic. And her role is the princess of friendship. Her whole thing is her friends. So when she became an immortal alicorn princess and her friends got old and died one by one, maybe something... snapped. She slowly lost her mind and Nightmare Sparkle started to take over!

Sytems like this are already in place for the show. Princess Luna becoming Nightmare Moon because she felt abandoned. Starlight Glimmer breaking time because she lost a friend. Sunset Shimmer going villain when she felt rejected. The difference is they weren't the literal embodiment of magic itself! So Twilight Sparkle becoming Nightmare Sparkle because all her friends died and left her behind to keep ruling.

Twilight started to destory everything, even the trust between ponies. Nightmare Sparkle is destorying (what is now) old Equestria, but in her final moments of clarity Twilight seals all the magic away to protect it, hoping the ponies of the future will be able to save everyone. And I mean ALL magic. Because without the power of friendship between pegasi, earth ponies, and unicorns the Windago will freeze everything and clearly nothing is frozen.

Then, she's gone. Either destorying herself or just going insane and eventually dying as Nightmare Sparkle.

Gen5 just... failed to solve the mystery

I cannot be the only one to have thought of this of course so idk I would love y'alls thoughts. And yes I heard about Opaline Arcana but I am not convinced she was the big threat that would cause Twilight to seal magic. She has dealt with WAY more powerful, angry, power hungry, dangerous threats before. I think Opaline Arcana was the show's weak excuse to quickly answer the question but never really knew how to expand on it.