The firewall was on, yes.
No other security apps.
I know about the importance of the SIP.
Not just one installer. I've tried a bunch starting with an app demo for musicians that I was interested in trying. Can't buy it if I can't install it.
The error log is mostly identical for all of them:
Sep 20 14:33:06 Mac-Studio-2 Installer[23503]: Failed to load specified background image
Sep 20 14:33:06 Mac-Studio-2 Installer[23503]: Could not load resource readme: (null)
Sep 20 14:44:21 Mac-Studio-2 installd[23983]: PackageKit: ----- Begin install -----
Sep 20 14:44:50 Mac-Studio-2 Installer[23503]: PackageKit: XPC error in -[_PKInstallClientConnection proxy]_block_invoke_2 (Error Domain=NSCocoaErrorDomain Code=4097 "connection to service named com.apple.installd" UserInfo={NSDebugDescription=connection to service named com.apple.installd})
Sep 20 14:44:50 Mac-Studio-2 Installer[23503]: PackageKit: Service connection invalidated!
Sep 20 14:44:50 Mac-Studio-2 Installer[23503]: PackageKit: XPC error in -[_PKInstallClientConnection blockingProxy]_block_invoke_2 (Error Domain=NSCocoaErrorDomain Code=4099 "The connection to service named com.apple.installd was invalidated: failed to check-in, peer may have been unloaded: mach_error=10000003." UserInfo={NSDebugDescription=The connection to service named com.apple.installd was invalidated: failed to check-in, peer may have been unloaded: mach_error=10000003.})
Sep 20 14:44:51 Mac-Studio-2 Installer[23503]: Install failed: The Installer encountered an error that caused the installation to fail. Contact the software manufacturer for assistance.
Sep 20 14:44:51 Mac-Studio-2 Installer[23503]: Displaying 'Install Failed' UI.
Sep 20 14:44:51 Mac-Studio-2 Installer[23503]: 'Install Failed' UI displayed message:'The Installer encountered an error that caused the installation to fail. Contact the software manufacturer for assistance.'.
Also neglected to mention that I did a complete re-install of Sequoia. No change.
Thanks.
KEv