This stuff does miracles...

Can't Cap just throw the Space Stone to the ground? It still counts as an infinity stone that "never left the timeline". Its just on another place, in another composition. Why does Cap need to put it back in the Tesseract form?

Also... one interesting thought... if Cap time travels, for example, to 1970, to retrieve the Space Stone, but hasn't yet retrieved the other stones to their times... then that implies the universe can survive or withstand two Reality stones, two soul stones, two power stones, two time stones and two mind stones, at least.

I don't see the problem with two stones existing at the same time. I mean, the stones from the MCU reality are not longer materialized in solid objects but they still exist. Energy is not created nor destroyed, it just transforms. The escense of the Stones is still a thing. Si we had 12 stones in the MCU by October 2023.

How it got into a cube before in the first place? I guess it has some feature like construct materials around itself. Like ice cube, just not by cold. Maybe its radiation changes nearby molecules automatically. Or you find Goose to swallow it then give back with packaging.

Used the time stone

Miguel Evaristo is right, though. Cap could just throw it on the ground without anything else involved, it just needs to be in the timeline, not where it was.

Now I have this image of Cap just dropping in for 5 seconds to toss a stone on the ground...then after the last stone, he says, “Maybe I should say “Hi” to Peggy”.

YES! That wouldn't complicate stuff XD

Hes a genius

He probably asked Ancient One to use the Time Stone and change the stones to their original forms. That's the most logical explanation.