This is due to code strings that they found in the upcoming macOS Catalina update in which it suggests that Apple TV+ will allow shows to be downloaded for offline viewing, but it could be somewhat limiting. According to the code strings, it suggests that it could be limited to how many shows in total that users can download in total.
It could also be limited to the number of times a show can be downloaded, or it could also be limited to the number of devices that a show can be downloaded from. For example, one of the error messages they found reads, “To download this episode of ‘The Morning Show’, delete it from another device and try again.”
The report adds that there could be limitations in the number of simultaneous streams at once, which isn’t to be unexpected as there are similar limitations with Apple Music and also other services like Netflix. Apple TV+ doesn’t have a set release date yet, but we have recently heard that it could be launching in November for $9.99 a month.