You don’t specify what you actually see and how you try to “fetch the IMAP remote folders list” but the default behaviour when Mutt is compiled with IMAP support is to list all folders. Presumably, your Mutt configuration contains changes from the default settings.
By default, when Mutt browses the list of available IMAP folders (e.g., after using
c to open another mailbox), it uses the IMAP LIST Command to retrieve the list of folders and the server returns all folders that exist for the user’s account.
To change this behaviour, the
imap_list_subscribed configuration option can be set to yes. In this case, Mutt uses the IMAP LSUB Command when retrieving folder names from the server: this retrieves only the list of folders that are marked as being subscribed on the IMAP server.
This variable configures whether IMAP folder browsing will look for only
subscribed folders or all folders.