Best version to run on a late 2009 iMac?

Yeah, so I'm a lifetime Windows guy and I picked up a late 2009 21.5 inch iMac for 40 bucks locally. 4gb ram, 500gb hard drive and Nvidia 9400M graphics. Running the latest version of High Sierra currently. I was looking into OCLP and running a newer OS for better compatibility with various internet software. Of course, Sonoma wouild be ideal but I've read something about severe graphical corruption on non-metal GPU's..that's way beyond me but it sounds bad. Is there a fix for that or should I look towards an older version? I'd appreciate the help

submitted by /u/Infinitrium
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