You can make your Steam profile transparent with a couple of game profiles. These game profiles make it so that you can see through the theme and show you more of your Steam background picture. Especially good paired with a artwork showcase.

It's actually really simple, all you have to do is have the 10k points to spend on the Steam point shop game profiles.
Steam Points Shop

Alternatively you can use:

Dying Light 2 is the best Steam game profile to have. This game profile is 100% transparent. Unlike some of the others I will mention afterwards. Make sure this is your first choice, as these game profiles do costs a lot(10.000 points).
DYING LIGHT 2 GAME PROFILE

Here's how it looks:

Puzzle Fest 2023 is also transparent, but not quite fully. Although it is around 98% transparent there is a red-ish color tint on the outlines of your profile.
PUZZLE FEST 2023 GAME PROFILE

Here's how it looks:
As you can see on the LEFTSIDE of the outline there's a bit of red.

Green House of Horrors is also transparent, but not quite fully. Although it is around 98% transparent there is a green-ish color tint on the outlines of your profile.
GREENHOUSE OF HORRORS GAME PROFILE

Here's how it looks:
As you can see on the LEFTSIDE of the outline there's a bit of green.