Mounting Full Motion Mount on a Single Stud
Toggles and other heavy weight drywall anchors can be suitable for TV mounts when the mount is flush. Or toggles in to metal studs. Since the load is mostly shear and not pull-out, this is fairly safe. (Provided the drywall is thick enough, the anchors are installed correctly, the wall is properly supported, and lots of other considerations too numerous to go in to here.)

However, adjustable, articulating or arm mounts should never be used on just drywall or metal studs. No matter what anchor you use, drywall and metal studs can not handle the pull out force applied when a TV is extended or tilted away from the wall.

So either get a flush mount, or open the drywall and install appropriate wooden studs.