This seems kinda silly, but I remember someone here was asking this exact product awhile back.
To be clear, this is for just the pillow and mounting arm, which can be used with various devices. For the steam deck specific mount, you’ll also need this, or their full steam deck bundle.
Alternatively if you have access to a 3D printer, they provide most of their designs here.
Interesting. I’ve personally never had a problem with my arms falling asleep, and this looks like it would force my arms into a weird uncomfortable position, but I’m sure there are some people who would really like this.