iosipswitunes
I'm looking for the public beta IPSW (specifically, the iOS 13 public beta 4), so I can update my iPhone via my Mac, instead of over the air.
https://ipsw.me does not seem to have them, and Apple Developer Portal only shows me the Xcode beta as an available download.
How can I download the software bundle?
Yes, you can download the update while tethered to the iPhone via WiFi. But to clarify, it won't ever automatically download the update without user intervention.
This article from OSXDaily details some further workarounds to this issue.
Yes, It will be possible to update to the iOS 8 public when Apple releases to the public. The update could be done via iTunes or OTA.
Best Answer
No, it's not possible to download the IPSW files for public betas of iOS/iPadOS 13. You can, however, download the IPSW of the developer betas.
To do so, you should be a registered member of the Apple Developer program enrolled into a paid membership. Once you have the paid membership, visit the Apple Developer Download page(s) below to access and download the respective IPSWs:
https://developer.apple.com/download/#ios-restore-images-iphone-new
https://developer.apple.com/download/#ios-restore-images-ipad-new