Flow currently has no support for Temporary accounts and adding such support was declined in T342831: Temporary Accounts: Update StructuredDiscussions (Flow) because we intend to undeploy Flow.
As undeploying Flow is a large project, in the meantime, it would be nice if we disabled interactions with Flow boards for not-logged-in users. This should be possible via the onGetUserPermissionErrors hook by checking if temp account creations are enabled, and if the user is anon.
This task proposes that anonymous users and temporary account users are not able to modify Flow boards--they will be in read-only mode for these users.