Great sign for Team USA Gymnastics ... Simone Biles just crushed the most difficult vault in existence during Olympic practice on Thursday -- and she made it look easy!!

The four-time gold medalist participated in the Red, White and Blue's practice sesh ahead of the 2024 Paris Games ... and based on the footage of the run-through, the rest of the world is in big trouble.

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Biles went through the floor and beam routines ... but when it came to the vault, she did a Yurchenko Double Pike (AKA Biles II) -- which is when someone does a back handspring onto the springboard and follows up with two backflips in a straight-leg pike.

It's widely considered the hardest vault ever executed ... and it's never been done at the Olympics.

It's great to see from the 27-year-old, who withdrew from the finals of the individual all-around competition in the 2020 Tokyo Olympics after she experienced "twisties."

The 4-foot-8 athlete detailed the mental struggle in a new two-part Netflix documentary ... saying it was truly terrifying. But now, she's back and ready to kick some ass.

"I knew it'd be a long journey," Biles said about her comeback, "but to me, it wasn't done."

If Biles wins two gold medals at the Olympics, she'll hold the record for the most by an American gymnast. Anton Heida currently sits at the top of the list with five.

The GOAT is back!!