My iPhone 11 keeps freezing when my alarms goes off.

That is not normal behavior.

First, make sure you have the most current version of iOS installed:

Update your iPhone, iPad, or iPod touch - Apple Support

If that does not fix your issue, take your phone in to have it examined:

Genius Bar Reservation and Apple Support Options - Apple

I would try to delete that alarm, then "force" restart your 11 using these steps:--> Force restart iPhone – Apple Support

When done, re-add your alarm and test it.

Regards

Giulio