Just an FYI because I think it might be a newer change, but the developer site is letting you download the IPSW to install iOS 13 even as someone who isn't paying for a developer account. Not as easy as the OTA profile, but it isn't difficult. I can also download the profile needed to get the macOS Catalina download. So it looks like Apple really isn't trying to keep anyone from playing with the software, there are some very low bars to trip over on the way to download things. Not like the hoops that used to have to be jumped through. There is just a note about being a thrill seeker and that you shouldn't install it as a non developer.