Snap store might simply be down. Too bad this stalls. Refreshing snapd is supposed to fix this (?) according to a solution I saw, but it does not work because the web API is down. I don't know if the API spec changed, but it is currently the case that the host is not resolved. You have to wait until the store is back up. PS: There was probably a server change which takes time to propagate in my case.
$ sudo snap refresh snapd
error: cannot refresh "snapd": cannot refresh snap-declaration for "chromium":
dial tcp: lookup api.snapcraft.io on 127.0.0.53:53: no such host
$ host api.snapcraft.io
;; connection timed out; no servers could be reached