Ubuntu 23.10 & Fedora 39, both running Gnome of all things (eye roll) run just fine on my late 2009 iMac (iMac 10,1)
nb : Fedora 39 has an installation bug. Installing Fedora 38 minimal then upgrading to 39 is the simplest solution. Kudos as usual to Canonical for shipping a trouble free install on Mac.