The game does a terrible job to teach new players how to heal.

[Nizzi]

I am doing mentor roulettes, and i ever so often get healers in my dungeon group that do no damage at all, they just stand around and do nothing or keep producing overheal despite no one taking damage.

I don't understand how it is not obvious that a healer also has to do damage if there is nothing to heal, especially on dungeon bosses.

That's exactly how they want the role played lmao, even in Endwalker Yoshida has said they don't see them ever adding more DPS abilities to healers because they don't want new healers to see more than 2 buttons and go "oh do i have to do damage while healing?"