2013 iMac 27” Help!!

Very new to this.. I’ve been gifted this 27” iMac, I managed to download Catalina using internet recovery as Maverick was too old.

I’ve managed to download OcLP, and then download the “install macOS Sequoia”, but it is telling me it’s not compatible with this Mac. Have I done something wrong? Or do I need a different version or a different OS?

Any help appreciated!!