Problems updating to Ventura or Monterey 12.6.x

I'm unable to update my MacBook Air (M1, 2020) from Monterey 12.6 to either Ventura or the latest version of Monterey (12.6.8), and I could use some assistance.

Last week, I tried updating to Ventura and found that the install would hang approximately halfway through. No error message, no crash, just stuck at "About 31 minutes remaining" with the progress bar at roughly 40-50%. I tried multiple times, left it for hours on end, and it simply never progressed. I tried booting into Safe Mode and running the install with the same result.

I did some research on this forum, and I found this post, which seemed like it was describing similar behavior. Based on the OP's comments, I decided to see if it might be successful if I first upgraded to the latest version of Monterey. But I'm seeing exactly the same behavior (at exactly the same point - an estimated 31 minutes remaining, with 40-50% complete) when running the Monterey 12.6.8 install. (I also realized that, although I have "Keep my Mac up to date automatically" selected in System Prefs->Software Update, my MacBook is still on v12.6, and I've not gotten any of the 12.6.x updates released in the last 10 months -- nor any messages telling me that fact. Grrr.)

Here is what I'm seeing in the installer log when I run the Monterey install:

Aug 14 12:19:16 Ryans-Air osinstallersetupd[946]: Syncing extracted data to disk

Aug 14 12:19:41 Ryans-Air osinstallersetupd[946]: Syncing extracted data to disk

Aug 14 12:20:52 Ryans-Air osinstallersetupd[946]: OSISDownloadOperation: No IAL update found.

Aug 14 12:20:54 Ryans-Air osinstallersetupd[946]: SFR scan failed, using bundled SFR: Error Domain=SUMacControllerError Code=7301 "[SUMacControllerErrorScanNoUpdateFound=7301] scan for SFR software update failed: [SUCoreError(Scan):kSUCoreErrorScanCatalogDownloadFailed(8400)_1_com.apple.MobileAssetError.Download:13]" UserInfo={NSLocalizedDescription=No available updates found. Please try again later., SUMacControllerErrorIndicationsMask=0, NSDebugDescription=[SUMacControllerErrorScanNoUpdateFound=7301] scan for SFR software update failed: [SUCoreError(Scan):kSUCoreErrorScanCatalogDownloadFailed(8400)_1_com.apple.MobileAssetError.Download:13], NSUnderlyingError=0x600002ea0b10 {Error Domain=SUCoreError Code=8400 "[kSUCoreErrorScanCatalogDownloadFailed] failed to download catalog (MADownload domain result:13)" UserInfo={NSLocalizedDescription=[kSUCoreErrorScanCatalogDownloadFailed] failed to download catalog (MADownload domain result:13), NSUnderlyingError=0x600002fb08a0 {Error Domain=com.apple.MobileAssetError.Download Code=13 "Download is not allowed as mobileassetd was starting up. (Catalog download for com.apple.MobileAsset.SFRSoftwareUpdate)" UserInfo={NSLocalizedDescription=Download is not allowed as mobileassetd was starting up. (Catalog download for com.apple.MobileAsset.SFRSoftwareUpdate), retryWithBackoff=true}}}}}

Aug 14 12:20:54 Ryans-Air osinstallersetupd[946]: AppleInternal: 0, Target contains Rosetta: 1, forced install: 0, validBaseBuild: 1

Aug 14 12:20:54 Ryans-Air osinstallersetupd[946]: Will require Rosetta update (fatal)

I don't have the Ventura install logs accessible right this instant, but I was similar messages, ending in the "Will require Rosetta update (fatal)" message in that log when running the install. (It was followed by a message about "Removing client SUUpdateServiceClient", iirc, but that one seemed pretty innocuous.)

Based on the above, it seemed like perhaps there's some problem with my Mac's Rosetta installation. So I updated/reinstalled Rosetta using Terminal (softwareupdate --install-rosetta), and I've verified that it's actually listed as installed in System Report->Software/Installations. It feels a lot like the installer is (for some reason) finding that Rosetta is not present, then waiting for me to install it as though it had popped up a modal message asking me to do that as described here.

I'm at a loss for what to do next. I've repeated this in both Safe Mode and normal boot mode, with no apparent differences in the error logging (at least for the Monterey update). The primary x86-architecture app I have running that would make a difference on startup is Dropbox, in case that matters. Any suggestions? Any ideas why I hadn't already been updated to 12.6.x in the background, or what I need to do to make sure that doesn't happen again? Thanks very much.