Mount 9KG 40" LED TV to a plaster wall with a cantilever mount, standing away from the wall?

For a plasterboard wall the strongest fixing is going to be by going into a stud, depending on where you're putting it and how big your bracket is you may naturally hit one stud but I doubt you'd hit a second. You could use a stud detector to find the nearest studs to where the tv is going, cut away the section of plasterboard in between them, enabling you to then run noggins between the two in the right position for your tv bracket. You can then replace the piece of plasterboard and make good, or leave it to the tv to hide it! You'll then be able to use screws straight to the studwork. If you don't want to go that far, then some spring toggles or hollowwall anchors would be the best fixings to use straight into the plasterboard, but with the above method you'll minimise the risk of fixings working loose or blowing the plasterboard later with the movement of the tv/bracket.

The bracket should have holes in which I'm sure are either 8mm or 10mm. You the put the bracket where you want it, check for level and mark holes. Using anchoring bolts to hold it in place. S&S Exterior Maintenance

Best bolts to use on plasterboard wall is anchoring bolts very strong used on a 55 inch on a moving bracket and had no problems