My kids are both actively playing TOTK on their profiles on my switch with a single digital purchase.

There have been other games where this has been problematic (Animal crossing I think limited some features per device instead of per account).

They can be downloaded to a switch and once they are on the switch an account playing that switch can play any digital games on the switch. They don't even tell you which account "owns" the game.

She bought digital and I can play it though.

Buying digital is worth it to me because I’m very disorganised and I will lose the cartridges

Some games simply have no stock of digital copies (at least not in the Netherlands). And haven’t had in months.