Flatpak steam can do all that. You just have to learn to control the flatpak sandbox. There are CLI commands of course or you can install Flatseal which is a real nice gui that lets you control the sandbox for each individual flatpak app. https://flathub.org/apps/com.github.tchx84.Flatseal
Just add whatever drive/directory/mount point in the filesystem path for Steam in flatseal and Steam can see it.
I couldn't get it going on anything but my steam deck to read SD cards. Flatseal doesn't seem to help. The only thing that worked after a ton of attempts following a ton of guides on my desktop was to get the deb version.
Flatpak steam can do all that. You just have to learn to control the flatpak sandbox. There are CLI commands of course or you can install Flatseal which is a real nice gui that lets you control the sandbox for each individual flatpak app. https://flathub.org/apps/com.github.tchx84.Flatseal
Just add whatever drive/directory/mount point in the filesystem path for Steam in flatseal and Steam can see it.
I couldn't get it going on anything but my steam deck to read SD cards. Flatseal doesn't seem to help. The only thing that worked after a ton of attempts following a ton of guides on my desktop was to get the deb version.