Is downgrading impossible on Android phones and tablets too? Never had an Android device … just curious to know. Anyone?
Technically it's possible with any Android device where you can unlock the bootloader, but in practice it varies:
- Pretty sure my Motorola support tools will let me install signed copies on my phone even after they stop showing them on the server, if I've got them saved. And that's just the official tools and ROMs, that don't require unlocking (because they are signed by the manufacturer). If I wanted to change to a third party ROM or AOSP (plain vanilla android) I could unlock my bootloader from the developer menu and do that. If I had a flagship device, there would be several third party ROMs to try and AOSP, but I don't, so that's mostly theoretical. But I can certainly keep a backup of earlier official copies on my computer. (I still have one I used to reflash my dad's Motorola phone a few months ago in case I need it again, and I was able to reflash just the system without losing his data, but don't expect that to always be the case.) I've also used a similar tool from Samsung to deal with my mom's really old Samsung phone.
- On the other hand, on my latest tablet by Chuwi, they don't have support tools they hand out to consumers. If I write to them and ask them, they'll post an archive with the current official build and installer for my device to their support forum, but they don't just have a file server up with all versions, supposedly because sometimes they change hardware while keeping the same model name. I can unlock its bootloader to install something else if I want, but nobody else has cared to try making a new ROM for it and I certainly am not going to try building AOSP by myself for it.
For your first Android device you may want to make sure you have a big brand like Samsung or Google, so you keep getting updates for a long while. You may want to pre-check
the device support list of LineageOS or another big third party ROM as well, in case you plan to keep it after official updates run out, so you can see how easy or hard it will be in general for your phone to switch later. And once you buy a device you may want to go ahead and download the current tool and official ROM to your computer just in case. Because the system function that checks for updates will automatically install them if you let it, or wait for you to approve, but it will never ever offer to go back.
P.S. Don't unlock your bootloader unless you need to. It's not the same thing as "unlocking your phone" from one provider to use on a different network. Some banking apps check the bootloader as a security measure.