Webhooks rely on the underlying API endpoint, so it’s impossible for them to provide any notifications to changes to an offline stream since the Helix streams endpoint does not return anything for an offline stream.
This is not something that can be changed as all existing apps using the Helix streams endpoint are built on the fact that no data returned represents the channel being offline, and to start giving data about offline streams would be a massive breaking change.
For the moment v5 is your only option to get that data, and in the future once v5 is removed you should consider not relying on offline stream titles as a source of information as there’s been no mention of that data planned to be made available in Helix.