Great that you like it.
The problem with reminders has been discussed here:
The main problem is the way timezones and the clock on your server works. Not an easy problem to solve but I will tackle eventually.
There’s the flutter app which should work on iOS but lacks quite a bit behind wrt features. It does not feature reminders (yet), PRs welcome. Because I don’t own a Mac, I can’t release it for iOS so you’d need to build and sign it yourself.
That’s a bit out of scope for Vikunja as it stands right now. This might change in the future once we have plugins but that’s not something with a high priority.