I don't have a PE 770 Brother, but I will bring this ttt for others. In my opinion, if you have a foot that the windneedle will work with, I do believe you can use it.

You can as long as it doesn't hit the sides of your foot.

ttt

You could check with a Brother machine dealer they should know!

Hold the needle in your fingers and check if it fits easily through the little hole in your stitch plate, if it does I am sure it can be used.

If your machine can do zigzag stitch you could use a wing needle. Should you have a stitch plate for straight stitch only, then you can't. My Brother 190D, which is a stand alone embroidery machine has a small round hole which would not allow wing needles nor twin needles.

Ditto what mops said.