Comment 2 for bug 1851250

As annoying as it may seem, this is a feature of the snap confinement, for improved security (the app isn't allowed to see files on the host system, except for non-hidden files and folders under $HOME and /mnt and /media (if the removable-media interface is connected).

This will be addressed in the future using portals, but the implementation isn't ready yet (see https://bugs.chromium.org/p/chromium/issues/detail?id=885292).

For your downloads, may I suggest a tmpfs mounted somewhere under $HOME ? I think this would achieve what you're after.

I'm marking this bug invalid as confinement is working as intended, despite the limitations this induces.