Painting over existing wallpaper could be problem if you ever want to remove the wallpaper at a later date. Painting over wallpaper seals it & will be a nightmare to remove. There is a product called Anaglypta, (manufactured in the U.K. but available throughout the US & Canada) this wallpaper is embossed & is great for covering up uneven or badly marked walls, it can then be painted any colour you like & as many times as you like. Good luck

Remove the wallpaper. Or remove the drywall and start over. Leaving the wallpaper, and ugh, texturing over it, is a hack move.

Crossline the existing paper with paintable liner using vov as the glue. Prime and continue with your desired finish.