I can reproduce it in Edge. I guess that's because Reader Mode is designed to provide a simplified reading experience, which may restrict certain interactions. But I also test on Chrome and Firefox reader mode and the page events will be fired.
I think it's by design in Edge and there's no way to handle the events on Edge reader mode for now. I suggest that you can request a new feature to Edge team by pressing Alt+Shift+I in Edge.
If the answer is the right solution, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.
Regards,
Yu Zhou