The standard "Close Date" field cannot be removed from any page layout for the Opportunity object, nor can the "Required" property be removed.
Check which fields cannot be removed by going to the "edit" page of your Opportunity page layout (see Customize Page Layouts with the Enhanced Page Layout Editor), and review the fields denoted by a blue dot. Hover over each and it will read "Always on Layout."
To check the Opportunity page layout, follow the click path below:
In Salesforce Classic
Setup | Customize | Opportunities | Page Layouts | Select the specific page layout
In Lightning Experience
Gear icon | Setup | Object Manager | Opportunity | Page Layouts | Select the specific page layout
Fields that cannot be removed
Quick Tip: Visit Close Date Required Field and Give option to remove "Always Displayed" fields from page layout to promote these product ideas by voting and leaving a comment.
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