Steam has it's own copy of mangohud in the launch env, that messes with locally installed version, you have to uninstall the local version for it to work in steam last I checked
I suspect you have installed either Lutris or Steam through flatpak.
Try installing both using the same method or install MangoHud both as a flatpak and a system package.
Also, I recommend enabling MangoHud with 'MANGOHUD=1 %command%' instead.
Have you tried with the --dlsym flag? Also check if mangohud works on the vkcube and glxgears demo first.
From Wikipedia, the free encyclopedia
Linux is a family of open source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991 by Linus Torvalds. Linux is typically packaged in a Linux distribution (or distro for short).
Distributions include the Linux kernel and supporting system software and libraries, many of which are provided by the GNU Project. Many Linux distributions use the word "Linux" in their name, but the Free Software Foundation uses the name GNU/Linux to emphasize the importance of GNU software, causing some controversy.
Community icon by Alpár-Etele Méder, licensed under CC BY 3.0