I configured the UI for my main. Then I clicked the cog on my alt, clicked Select Client Profile, clicked Manage Profiles then clicked Copy Profile with my main profile selected. I got a new profile on the right side (Tranq). I renamed it to my alt. I clicked close. I selected the new profile from the drop down. I clicked Apply.
I logged in my alt. UI is completely different, default setup, none of the configuration settings for my main appear in it.
Copy profile applies to a bunch of launcher-hosted settings, not in-game settings; those live elsewhere. I don’t recall where off the top of my head, and it’s been made MUCH hard to port them between characters and clients than it used to be.
I believe that is currently the case, yes - but if it works the same now as a year-ish ago, you can control client display settings (graphics, sound, window position, etc) on a per-account basis by assigning them to specific profiles. For example, having account A launch full-screen windowed with high-end graphics settings and all sound enabled, while account B launches in a small window in potato mode with only specific audio piped.