Transactional Replication data during rebuild
The reporting DB no longer contains data but only views that replicate the structure of the tables in the data repo. During a rebuild of the "data repo" database the "reporting db" is set offline


Yes, that's reasonable.  You can further optimize this approach by pointing the users to a snapshot or restored copy of the subscriber database during the downtime, eg per https://techcommunity.microsoft.com/t5/DataCAT/Microsoft-SQL-Server-Database-Snapshots-and-Synonyms/ba-p/304987, or by reinitializing the subscription from a backup, which might be faster than using a snapshot.

Or you could just disable the reporting users logins and kill their sessions during the downtime.