I had iMac in ~2009 had to do virtualisation work, so tried to upgrade RAM, ordered a few RAMs and none of them worked, iMac refused to boot. Gave up on this,

I had iMac in ~2009 had to do virtualisation work, so tried to upgrade RAM, ordered a few RAMs and none of them worked, iMac refused to boot. Gave up on this, never used Apple products again... too much hassle and too much lockdown from manufacturer.