I think your tile gives you a great, simple background to build upon. I would start with removing the tub’s glass doors and frame. I have removed two or three of them and found the track was just caulked to the tub and there were only two or three screws on the side walls. Get color-matched caulk for the holes in the tile. You may want to look into modern glass enclosures. Some have a stationary panel and a hinged door. Others are bypass sliders, but you should be able to find something without that infernal track.

Next, I would remove the wallpaper and replace it with something you like. Your color options are vast, just please don’t try to pretend that the warm beige base color in your bathroom is a cool gray. So many people refuse to embrace their beige and try to turn it into something it is not. You can go greens, blues, maroons, reds, peach, so many colors. Just try to get a bit of your tile color in the print and you won’t go wrong.

Nancy has good ideas. I’d also switch out the tan toilet seat cover with a white one.

If you like kitchy themed wallpaper for a giggle, here is an ocean-themed one:

Beige Ocean Life and the colorful version may work, too.

This textured stripe might work, but maybe not. It might not look that good above the tile, itmay need to also be on a full wall. Taupe gradient stripes

If the beiges match your tile, this stripe would bring blue into the room Blue and Beige Stripe

Here is a beigey stripe that might match. Be sure to avoid a yellow background color, as that is what I dislike about the paper that is up there now.

So you get the idea. These were just the beachy-type papers I looked through at Wayfair. There are florals and botanicals, too. Something with Navy would probably go well, with Navy towels and accents.