How can I remove religious holidays from the Calendar app on my iPhone 8?

duderay wrote:

How do you remove the religious holidays on the Calendar app on my iPhone 8.

You don't. You are using what is called a subscribed calendar, which cannot be altered. You can look for another subscribed calendar or install a fully customizable calendar app from the App Store.

Here is how you can subscribe to different calendars, but whichever calendar you subscribe to, cannot be altered --> Use iCloud calendar subscriptions - Apple Support

Here is a location where you can choose to subscribe to different calendars or create your own calendar subscription.

https://www.calendarlabs.com/ical-calendar/

As stated subscriptions cannot be altered, but that does not stop you from creating your very own Calendar that is not a subscription and add any event you want to it. You can call it whatever you want and unsubscribe from the current Holiday Calendar subscription. You are not required to use any Calendar Subscription.