Is the scorpion OCP approved for Army use? Can I buy them and wear them to replace my Multicam OCP?

Mulricam was authorized until SCORPION (OCP) was fully developed and fielded, but only because the pattern was so close. Now OCP should be the only authorized pattern, and I believe active ditty should have been using clothing allowance to replace the older patterns. RC would have had an issue sometime last FY
FYI

Operational Camouflage Pattern (OCP), originally codenamed Scorpion W2, is a military camouflage pattern adopted in the mid-2010s by the United States Army for use as the U.S. Army's main camouflage pattern on the Army Combat Uniform (ACU). This pattern officially replaced the U.S. Army's previous Universal Camouflage Pattern (UCP) as the official combat uniform pattern for most U.S. soldiers at the end of September 2019. The pattern also superseded the closely related MultiCam, a pattern previously used for troops deploying to Afghanistan. The United States Air Force is also replacing their Airman Battle Uniform with the ACU in OCP after positive feedback from airmen who wore the uniform while being deployed to Afghanistan with Army soldiers.

The Multicam (OEF-CP) uniform pattern was phased out alongside the UCP pattern. It is highly recommended you purchase the new OCP uniforms.

Wasn't that phased out last month? I'm surprised your leadership didn't "Strongly recommend" you get the new ones.

Does the uniform still allow the full color American flag or the faded green one?

Scorpion (the only Army OCP) is now mandatory for Army use. Multicam (by Crye) is no longer authorized (possibly with a few exceptions). You can tell the difference by looking for "vertical" elements (simulating upright branches) in the mostly horizontal pattern. Multicam has them; Scorpion doesn't.