I can't find any snap app after I update the system

Canonical doesn't want users to discover snaps this way anymore.

snap find

now returns this error:

error: cannot list snaps: empty query

According to Canonical’s John Lenton:

“snap find” without arguments has not shown “all available snaps” in quite a while; it would show 100 arbitrary snaps. That is expensive and never what the user wanted, so in 2.11 we stopped doing that.

Having ‘snap find’ return all snap packages is expensive, both on server resources (to get, collate and serialise everything), network bandwidth (to transmit the dump), and client resources (to display all of that). It would also force us to support pagination of the store queries in snapd, and of snapd responses.

Workaround

snap find .

Explanation:

You need to pass an argument to the snap find command. The argument can be either the name of a snap package or a regular expression to return a list of packages matching the regular expression as in the above example command.