Reminders
How can I recover deleted reminders on an IPhone 12 Pro?
iPhone 12 Pro, iOS 14
You will have to restore them from a backup that has those reminders:
Restore your iPhone, iPad, or iPod touch from a backup - Apple Support
Beware that restore is an all or nothing process. You cannot restore only reminders (for example) and any information on your iPhone between now and when the backup was created will be lost.