This app was mentioned in 7 comments, with an average of 1.71 upvotes
I already tried app like this, Floating Toucher, but I don't want any further button, just one movable button with gestures.
Image is how it works on Flyme roms.
https://play.google.com/store/apps/details?id=com.boatmob.floating.touch
https://play.google.com/store/apps/details?id=com.boatmob.floating.touch&hl=en
it's not messenger