That's a good call, I'll try that (even though both of us know it's probably speficific to the screwed migration).
40Gb (8+32) if I'm not mistaken. And yes, everything is off the internal (non Fusion of course, bleh) drive.
Yes with 40GB RAM and an SSD (I didn't realize Fusion drives were the base config as late as 2019...) you should be fine hardware-wise to run even Sonoma. So far consensus is that it uses more resources than Monterey but not that much more (16 GB probably fine, 32 more than enough so 40 should be a non-issue).
It does seem likely based on what you've said that something came over with your user profile that isn't sitting well with Sonoma. If it was just Safari, I would suggest cleaning out the Safari preferences/etc stuff:
~/Library/Safari
~/Library/SafariSandboxBroker
~/Library/SafariSafeBrowsing
~/Library/SafariSandboxBroker
~/Library/Preferences/com.apple.Safari.SafeBrowsing.plist
~/Library/Preferences/com.apple.Safari.SandboxBroker.plist
~/Library/Preferences/com.apple.SafariBookmarksSyncAgent.plist
~/Library/Containers/com.apple.Safari
~/Library/Containers/com.apple.Safari.BrowserDataImportingService:
~/Library/Containers/com.apple.Safari.CacheDeleteExtension
~/Library/Application Scripts/com.apple.Safari
~/Library/Application Scripts/com.apple.Safari.BrowserDataImportingService
~/Library/Application Scripts/com.apple.Safari.CacheDeleteExtension
~/Library/Caches/CloudKit/com.apple.Safari
~/Library/Caches/com.apple.Safari
~/Library/Caches/com.apple.Safari.SafeBrowsing
~/Library/SafariSafeBrowsing
~/Library/Cookies/com.apple.Safari.SearchHelper.binarycookies
[Note deleting all the above folders files will delete all your bookmarks, history, preferences, website exceptions/blacklists, etc).
However if the issue is bigger than Safari (but not system-wide), your two basic choices are to do a lot of debugging across your existing profile until you find the thing(s) to replace/rebuild/delete/etc (Activity Monitor may provide some clues here) or create a new profile and manually migrate yourself over.
Assuming the computer works well under the clean profile and you go the latter route approach above, you probably don't need to reinstall the OS or any application under /Applications again. Basically just recreate their preferences/etc. However to your point sifting through all those settings and preferences to recreate them under a new profile may be as time consuming as anything...