I got bit by this with iPhone backups. I did a phone trade in and followed the backup before trading in instructions. Problem is after the trade in the backup failed to restore due to an unknown error. The whole manual syncing and backing up with a cable workflow with Apple is super fickle and riddled with bugs.
Luckily I had Time Machine backups of my iOS backups and I managed to avoid losing too much data.
As a sidenote it seems like Apple has pretty much neglected their offline backup and syncing workflow to drive more people to just pay for iCloud storage. Half the time my iPhone takes hours just to get detected by the mac when plugged in.
Man, Time Machine can fail just as badly. Unknown errors and there is no help or documentation or way to fix it. Carbon Copy Cloner [0] is the way to go for retaining sanity. Absolutely excellent documentation for pretty much any use case. And it works reliably. Not affiliated but after having had terrible experiences with Time Machine I feel compelled to bring it up every time I come across the topic.
While I don't like how annoying Apple is with service upselling (iCloud, Music, Arcade), at least they moved iPhone backup from iTunes to Finder. So their local iPhone backup process is being maintained over time.
I don't have issues with my computer (PC or Mac) detecting my iPhone. Generally need to make sure iPhone is unlocked after plugging it in. What is tough is the large size of my iPhone (X gb) and how small my Mac's HD is (2X gb).
I’ve changed iphones many times and the issue still persists for me. The only reliable way to get photos synced or iphone deteced in finder is to turn on airplane mode for some reason. Must be a bug with wifi syncing.
You actually bring up another issue. There is no obvious way to backup iPhone locally to an external hard drive. So either pay the mac SSD storage tax or the icloud tax.
Luckily I had Time Machine backups of my iOS backups and I managed to avoid losing too much data.
As a sidenote it seems like Apple has pretty much neglected their offline backup and syncing workflow to drive more people to just pay for iCloud storage. Half the time my iPhone takes hours just to get detected by the mac when plugged in.