There is an option to change the default reminders, but they are very hidden; I've submitted a feature request with a proposal to make them more visible here: https://morgen.canny.io/feature-requests/p/default-reminders-are-very-hidden

In the settings each calendar has reminder settings. Are you getting reminders for calendars that have none set?

Very important.

Definitely a feature that needs to be added. I'm new to the app, and am not sure how bothersome it is, but Samsung calendar has the option to change default reminder settings, and im glad it had, since every event popping up on my screen like an alarm was pretty lame, and manually taking it away on each created event is not too much effort, but it could save an unnecessary step