Christopher, you wrote "They were NOT in iCloud". have you checked, if iCloud Photos is still turned off? I am asking, because the only way I haver have lost all albums and folders has been because of iCloud syncing. On some system versions iCloud Photos has become enabled automatically by default after a system upgrade, if we had an iCloud+ subscription and we may not notice it for a long time, because there is no warning. If you have not done so and recently upgraded an iPhone or iPad, check, if iCloud Photos is still disabled on all your devices, as it should be.
It is has been some time ago, but all my albums and folder vanished from Photos for Mac, after I enabled iCloud Photos on my iPad.
You also wrote "While some of the albums came from iPhoto, "
Have these albums been in a folder called "iPhoto events"? The albums in this particular folder has been behaving strangely, not like the albums we created ourselves, like Photos were treating the iPhoto albums in a special way. To avoid these problems I have recreated all older iPhoto albums outside the "iPhoto Events" folder. I have not had any iPhoto Events albums any longer in my library after macOS 10.14 Mojave. Perhaps Apple has removed this folder automatically on Ventura, when it has no longer been possible to migrate iPhoto Libraries to Photos and could no longer create iPhoto Events albums and folders.