In sleep mode, my Android ROM shows me notifications like this: screen off > screen on with a line for the notification, colors of the screen in black & white for less consumption and low brightness > 10 seconds and screen off. I like this.
Textra, by overriding this built-in​ system, turn on the screen, full color and full luminosity, and turn off after the screen on duration specified in the phone settings, 1mn for myself.
I must add that I disabled floating notifications in Textra settings.
What I'd like is to tell Textra to just use the Android system notification engine if I want to and have the notifications work like for any other app.