I would conclude from this that your dc-dc converter is out of whack and only works stable enough for a small range of input voltages. This hardware issue might require a hardware fix at a repair shop :/
Most of the time, your grub is still there, even the link on your efi partiton. Only the evivars in uefi need to be reminded of their existance far too often.
You look at your DE all day and your distro holds everything together. Op didn’t say distro is unimportant and I agree it makes sense for new users to look at images and videos of different desktops first, maybe try a live cd, and then choosing the backend that suits their willingness to interact with.
If your electricity and time are cheap, you want to learn and your pc-system is your playground not a productivity tool, Gentoo is a valid option. In this case, your choice of DE impacts your compile time massively and knowing alternatives beforehand gives you options.
Would you notice if it doesn’t? The screen flickering is obvious, what if your ram and ssd flicker, too? You can tinker with that laptop and try to reduce 3.3 or 5v power rail load with kernel flags, but until someone checks those power rails electrically I wouldn’t trust that laptop to be reliable for anything but a tinkering exercise. We sadly don’t get redundant power IC’s you could switch to, but the failure is common and the involved parts cheap. I wish competent repair shops were more common.
If you consider the human brain works in 90 min chunks for most things including sleeping, that is completely within spec. For another chunk of sleep, you need to go to bed 60-80 min earlier.