Sharepoint - How to Make Fields Required in Edit Form

A simple solution:

We create a list validation that only executes in the edit form, not in the new form. For this, we compare the date of creation with the modification date. If they are equal, it is the new form:

Formula:

=OR(Created=Modified;AND(Created<>Modified;NOT(ISBLANK([test 1]))))

Source with images: Surpoint