Use Target display mode on (27-inch, Mid 2011)

Review the document: Use your iMac as a display with target display mode - Apple Support

Target display mode is a feature available with late 2009-Mid 2014 iMacs. The display Mac has to be running macOS High Sierra or older and the signal producing Mac has to be running macOS Catalina (ca. 2019) or earlier.

Is your Mac providing the signal also meeting the requirements I (and the article) outlined? If this is a relatively new MacBook Pro then no.

If the Mac using it is in the right date range also.