connect mini to iMac display

What year model Mac Mini?

see > https://support.apple.com/en-us/HT201894

While you're 27" Late 2013 iMac does support Target Display Mode.

No new Mac or Mac Mini running Big Sur, can use an iMac as a display.

please carefully read > https://support.apple.com/en-us/HT204592

You're welcome.

You can however, use most any aftermarket display with the Mac Mini.

see > https://support.apple.com/guide/mac-mini/connect-a-display-apd8e4fbbb97/mac