making it a per-profile settings does not exclude making it available per-device or per-visit. it's not especially difficult to store a flag in localStorage or a cookie. hell, you can even use CSS to detect OS dark mode preference settings and have it change automatically with no user input at all.
I just want them to follow system default for guest user(s).
they probably require an account because they have a system set up in a way where it's mostly a server-side app and ui settings are only stored on the server
This makes more sense for signed in user(s).
No dark mode unless you register, is what I consider to be a asshole design choice.
Ok, made an account(used a temp email). Nothing exquisite, just being able to switch between light and dark mode. I expected an option to set the toggle to follow device default after making an account and signing in.
Doesn't even remember which mode was toggled during the previous sign in.