Error on migrated New item form - SP 2019 to Online

I have started migrating forms from SP 2019 to Online. The first forms I am migrating are for a calendar. I have exported and then imported the forms using the forms designers to the migrated list.

The Edit and Display forms work as expected, however, I am receiving the following error when loading a New item form:

I have commented out all custom JavaScript to eliminate that.

Hello @Andrew,
How are you performing the migration? Are you using the import/export functionality from the form settings?