Or should i log in to work on weekends and holidays to make sure their aren't any missed messages?
Definitely. Just make it a habit to check your messages daily, it seems like this is what your manager is expecting you to do.
No, not daily - just on work days. if you're not paid for weekends, you don't do any work on them, which includes reading email as that is something that you should be on the clock for.
My job is the same way. I can't log into and check anything unless I am clocked in. It is 100% a terminable offense.
I'm not sure how Discord severs work, but from her phrasing, it doesn't seem like OP would be locked out if she's not actually scheduled to work. I realize she shouldn't have to "work" when she's not scheduled! If the only way, though, to learn about the meetings is to take a couple of minutes to check her messages, I'm not sure I see the problem.
It's my understanding that there are workplaces like restaurants where you have to call in for your schedule (via a computer app or actually calling the store) I'm not sure I see a difference here.