• Snap runs in a sandbox.
• Permissions of the sandbox are defined in the package itself
• when possible install from channel --stable which typically offers the app enough permissions to run normally
• if not possible to install as stable install with devmode to be able to read files…or something
• it appears Snap apps can't even see certain directories like /tmp and /home. Symlinks don't fix the problem. Instead the files need to be copied somewhere else, such as /var/tmp

workaround for snap not able to access outside of /home

mkdir /home/you/tmp
sudo mount --bind /tmp /home/you/tmp/

# <file system> <mount point>   <type>  <options>       <dump>  <pass>
/tmp        /home/you/tmp   auto    bind    0   3

sudo update-initramfs -u -k all