Videos and photos are already compressed to an efficiency sweet spot. Compressing them further really is a last resort solution that doesn’t make a lot of sense compared to all the other alternatives. You’ll gain 30-50% of your space back which isn’t enough to solve the problem but you’ll lose valuable data.
You actually had a lot of choices here, many of them are better.
You can sync iPhones with a cable to a computer like the iPod days and have the phone automatically delete photos that are synced with the computer to save space (this might require a Mac with Photos app, but I am pretty sure the PC version of iTunes can sync in a similar way).
(“Whatever iTunes is called now” is generally irrelevant on the Mac side, manual syncing functionality has moved to Finder)
You can obviously use an entirely different photos application than what Apple provides, including self-hosted solutions and competitors like Google.
You can also advise your mum not to make the dumb upgrade of going from an iPhone X to an iPhone XS with smaller storage. It would be better pick up a used iPhone 11-13 with upgraded storage at a very reasonable price, should be under $400. If you don’t upgrade to a smaller phone you don’t have this problem: you can make an exact clone of the existing phone to the new phone with the migration tool with or without iCloud.
Or you could get a phone like a Samsung A series with a microSD slot and pay under $400 for it. iPhone users seem to act like they have to choose between an extremely expensive phone or a beat up hand-me-down that barely functions, but they could just stop buying iPhones as another alternative to save money.
Let’s not forget that the fact that we are having this discussion means that your mum is depending on local phone storage to keep data safe, I imagine she ain’t doing 3-2-1 backups. So really she should be using iCloud or another cloud provider regardless of her phone storage situation.
I completely and fully understand that non-technical people want a seamless, affordable experience.
However, there is some point where the user is responsible for having a brain making a sensible decision. I’ve gone through this situation with relatives over and over: they never want to spend a damn dime on technology, they don’t understand why they should spend $3 a month to keep their family photos safe on professionally managed cloud storage, and then they refuse to use any technology besides busted hand-me-downs that aren’t adequate for their needs.
And it’s not ever about the actual expense, because if it was they’d cancel their $20 a month landline that they never use or stop trading in their car as soon as it hits 100,000 miles or gets paid off.
They are wildly frustrating about this. They don’t want to use cloud storage but then I’m the IT department when managing files manually is too time-consuming and difficult.
My relative’s email
is filling up because they’re using email to send family photos around and even email them to themselves to save them since they refuse to use “the cloud.” So basically they’re using the cloud anyway because they’re using email as storage instead of a proper photo solution.
Long story short, Apple (and Google and Samsung and everyone else who makes the same product) already gave you and your mum the best, most convenient, and safest solution, but there will always be stubborn people who feel like that’s not good enough and that it’s a money-grabbing scam because it has the one downside of costing a reasonable amount of money per month.
“I don’t want to buy a phone with big storage, I don’t want to buy a phone that has a microSD slot, actually I don’t want to buy a phone at all I’ll just use yours when you’re done with it, but why can’t this stupid phone hold all my photos? What do you mean backup? Are you saying I lost my photos!? Apple/Google/Samsung are a scam!!”