SharePoint Online bug breaking classic form customization

According to SharePoint’s major update announcement MC222880, the following two classic form customizations will no longer work when a list or library is configured to use the modern SharePoint experience:

• Web parts on a form page, such as a Content editor web part.
• Form fields with JSLinks.

The roll-out of this update happened in early November 2020. This update was only supposed to break customizations created after 10/25/2020, but it turns out that customizations of any date are affected. At Lialis we experienced this bug as well, with our SharePoint Online apps that use the Classic version of Shareflex Forms.

Fortunately, there are three easy solutions:

Option A

For every affected list/library, set the List experience (under List/Library settings > Advanced settings) to “Classic experience”.

Option B

Activate the “SharePoint Lists and Libraries experience” Site Collection Feature. This will change the default list/library experience from Modern to Classic.

Option C

Set the EditFormUrl / NewFormUrl / DispFormUrl content type properties to the URLs of your custom forms. This allows you to keep using the modern SharePoint experience.