newest version of macOS for 2009 imac

Sorry, no. See the following from Identify your iMac - Apple Support

iMac (27-inch, Late 2009)

Model Identifier: iMac10,1

Part Number: MB952xx/A, MB953xx/A

Newest compatible operating system: macOS High Sierra

Tech Specs: iMac (27-inch, Late 2009)

User Guide: iMac (27-inch, Late 2009)

iMac (21.5-inch, Late 2009)

Model Identifier: iMac10,1

Part Number: MB950xx/A, MC413xx/A

Newest compatible operating system: macOS High Sierra

Tech Specs: iMac (21.5-inch, Late 2009)

User Guide: iMac (21.5-inch, Late 2009)

No, the most up-to-date macOS supported by iMac 2009 is High Sierra. If you don't like, downgrade to El Capitan, which is still a big favorite.