I stop all the work, I end every frame, I flash in a storm, I change up the game. What am I?

I have keys but no locks, I have space but no room, You can enter, but not walk through.

you use it as a door, but it has no handle. it is theoretically possible to create, but nobody knows how to create it.

Invisible, I fill the space, no weight to hold, no shape or face. I slip through cracks, yet hold you tight, I hug you close day and night. I feed the flames and paint the sky. You see me not, but feel my touch, essential, yet you can’t clutch.

They walk over; they walk under; in times of war they burn asunder