softwareupdate --fetch-full-installer --full-installer-version 10.15.3
You can still download 10.15.3 with
Code:softwareupdate --fetch-full-installer --full-installer-version 10.15.3
or with gibMacOS https://github.com/corpnewt/gibMacOS
See this thread for how to use it https://forums.macrumors.com/thread...led-on-me-several-times.2215873/post-28073346
Sorry, I forgot that command only works in Catalina. Unfortunately, the similar command that was supposed to work in Mojave (open "x-apple.systempreferences:com.apple.preferences.softwareupdate?installMajorOSVersion=10.15.3"), does not allow the download of 10.15.3 at the moment.That requires 10.15 installed before to be installed
The script downloads the components from Apple and builds the Install app. If you don't trust it, you can do that yourself by following the commands from the script. You can find the links in Apple's update catalogGetting a Mac OS release from anywhere other than Apple is never a good idea IMO.
https://swscan.apple.com/content/catalogs/others/index-10.15customerseed-10.15-10.14-10.13-10.12-10.11-10.10-10.9-mountainlion-lion-snowleopard-leopard.merged-1.sucatalog.gz
http://swcdn.apple.com/content/downloads/01/28/061-86291-A_JPEIWIOZES/enpozvvbmj3mj2dhulhevlt8b429qd5kw0/BaseSystem.dmg
http://swcdn.apple.com/content/downloads/01/28/061-86291-A_JPEIWIOZES/enpozvvbmj3mj2dhulhevlt8b429qd5kw0/InstallESDDmg.pkg