> in order to keep the warranty, you have to visit an Apple-approved repair center to have a specialist perform the upgrade, which costs more than doing it yourself
At least in the US (and presumably in the EU which is much better about this sort of stuff) this is not legal. You can upgrade it on your own and Apple still has to honor the warranty.
I've done user-upgrades of the RAM on all my desktop Macs, and subsequently had repairs done under warranty here in the UK. Never had a problem and one at least two occasions the Apple engineers knew about the RAM upgrades. In fact the last HD replacement on my iMac was done free even out of warranty, I think because I mentioned I'd had it happen before on a previous Mac.
At least in the US (and presumably in the EU which is much better about this sort of stuff) this is not legal. You can upgrade it on your own and Apple still has to honor the warranty.
https://www.ftc.gov/news-events/press-releases/2018/04/ftc-s...