I am now running ESXi 6.5 on HP ProDesk 600 G4
Couldn't get it to work with UEFI/GPT boot partition (BIOS is likely to blaim), so will stick with Legacy/MBR
Was able to find a workaround for "formatwithmbr" option not working (partition still being formatted for GPT): install ESXi 6.5 version instead
Didn't upgrade to 6.7 yet, but see no reasons why it shouldn't work