You’ve got the right folder, but I suspect the wrong thinking about the filesystem on Linux. If you have multiple distros on your PC, in a multiboot fashion, then the Mailspring folder you want is actually on a separate partition from the one you’re linking on.
/home lives on the partition of whatever distro you’re booted into. It isn’t shared between distros by default, unless you’ve actually configured them all at install-time to have a shared dedicated
/home partition (which isn’t advisable, incidentally).
What you need to do is configure the partition that houses the Mailspring settings you want to be accessible from all the other distros. Set up a mountpoint for it, if it doesn’t have one already. Auto-mount it.
Let’s assume you have mounted it to
/mnt/common-home. Then you would link something like this:
ln -sf /mnt/common-home/home/user/.config/Mailspring ~/.config/Mailspring
Of course, I’m making a wild guess about the file system on that
In the end, this is a Linux partition configuration issue, not a Mailspring issue.