I have been backing up my work on an HDD for a long time now. I have archived nearly everything I have made (including lots of physical and school stuff) and I may plan on getting a bigger one soon seeing as my current one is kind of old at this point.

As for backing up iOS and Android files plugging them into your computer and then transferring them onto your desktop hard drive is a solution if you have both. people who exclusively use Android devices also have swapping SD cards so using SD cards is a good option even if they're easier to lose.