Dial, Safe Mode worked. I d/l'd Monterey first and then Ventura. No problems, so thank you for the solution
I ran Etrecheck: no major problems, a few minor ones: unsigned software (brought over from another machine -- I deleted it), and a report of numerous app crashes. I'll paste in the crash reports in case they're useful, but don't feel obligated to go through with them.
It seems off to me that I can't update/upgrade the OS; if it happens again, I'll have to dig deeper. I bought this machine in 2021, but I haven't started using it until just recently. There shouldn't be any junk on it, and I've made only cosmetic adjustments.
Regards, and add to your stack of points!
<snip> from Etrecheck report:
Diagnostics Information (past 7-30 days):
2023-07-20 07:03:08 suggestd - High CPU Use
Executable: /System/Library/PrivateFrameworks/CoreSuggestions.framework/Versions/A/Support/suggestd
2023-07-19 22:58:56 Fantastical Widgets - Crash (7 times)
Executable: /Applications/Fantastical.app
2023-07-19 20:34:53 Fantastical App Intents - Crash
Executable: /Applications/Fantastical.app
2023-07-19 20:22:48 PerfPowerServices - Crash (62 times)
Executable: /usr/libexec/PerfPowerServices
Details:
libsystem_c.dylib: abort() called
2023-07-18 23:14:11 installd - High CPU Use
Executable: /System/Library/PrivateFrameworks/PackageKit.framework/Versions/A/Resources/installd
2023-07-18 11:17:54 signpost_reporter - High CPU Use
Executable: /usr/libexec/signpost_reporter
2023-07-13 11:28:20 OnyX.app - Hang
Executable: /Applications/Utilities/OnyX.app
2023-07-13 11:17:03 triald - High CPU Use
Executable: /usr/libexec/triald
2023-07-13 07:46:05 com.apple.preferences.softwareupdate.remoteservice - Crash