Functionally, not really. I can get my work done on anything from FVWM to GNOME without a hitch.

Aesthetically, very much. The Chicago95 theme sparks joy and makes work just a bit more enjoyable. KDE and GNOME might have more creature comforts, but I will happily tolerate XFCE because it works well with Chicago95. I don’t even do fresh installs anymore because of the time it takes for me to configure the visual style just right. I’ll instead image from an install I’ve prepared on a VM.

In matters where the judgement of the courts cannot be trusted and I would be jailed either way, I’d rather have the option to wipe my phone.

Between 2 and 3. I’ll show off my Linux setup to friends and preach to the choir, but I won’t rub my choices in the faces of people who use other distros or operating systems.

Certainly. I’ve had setups with FVWM as a pure window manager while using XFCE’s xfce4-terminal, MATE’s Caja file browser, and GNOME’s Evolution mail client. Some utilities will pull a few extra dependencies from their native DE, but they won’t get in the way either.

Display manager won’t matter too much, most should be configurable to point at your WM of choice. LightDM integrates nicely with GTK themes, SDDM for Qt, and GDM for GNOME.

The biggest pain point from my experience was configuring power management and lid close actions manually, if using a laptop, since those often are only done for you if you install an entire DE at once.

Also grab a copy of qt5ct if you’re interested in making your Qt packages look more integrated next to GTK packages.

Worth it, especially if you are stuck with the phone. Find FOSS equivalents of the built-in utilities (gallery, files, etc.), disable what you can (judiciously) with uad-ng, block the apps that can’t be disabled from network access using Rethink DNS, and use the websites of services on a computer browser instead of apps whenever possible.

It’s still far from what privacy ROMs can do for you, but until you can get a GrapheneOS, etc. friendly phone, taking some action is much better than just letting the spyware run wild.

No idea about macOS, but this is something the typical Windows user should notice when switching over to Linux. That is, Windows OOBE gives you a user with administrative privileges by default and therefore won’t prompt you for the password again after logging in, just yes/no dialogs when exercising those admin privileges.

Typing in the password whenever you need root privileges is just part of the security model of Linux and unless for some reason you’re using sudo for everything, people get used to it. Your default user account doesn’t automatically have root privileges, sudo or su mediates that for you. Back when I used Windows, I even had my accounts set up that way, separate admin, daily user account without admin privileges, and prompt for the admin password every time I installed stuff, etc.

Granted, it does leave me with a couple compromises like a login password that is shorter than my disk encryption password so I’m not asked for the full thing every time I sudo and sometimes leaving a terminal with sudo -i hanging around.

Linux Mint is your best bet. Intuitive for new users without any flashy features to get in the way.

All said, temper your expectations. I did this for a couple of my folks and the Linux partition just sat untouched until I next visited (and presumably thereafter). Despite updates for their existing Windows 10 ending. For an unfortunate majority of people, they don’t really care until their browser stops rendering pages, no matter how you proselytize Linux.

If you are passionate enough and have some money to spare, get a used laptop (240 GB SSD, 8GB of RAM, 3rd Gen i5 at a minimum), preferably enterprise-grade (Latitude, ProBook, ThinkPad), clean it up, and pop Linux Mint onto it. Your folks can then experience Linux at their leisure, side-by-side with their existing machine at no risk. No fussing with boot order menus, which I have seen confuse computer science graduates.