@AngryPenguin I checked the ISOs from 16.11 (#'s 481, 480, 477 and 478) and found they boot Legacy or UEFI on my desktop (Ryzen5 3600) with no problem In VirtualBox they boot Legacy OK. If user wishes to use EFI boot in VBox they boot to an interactive shell where you enter a few commands to EFI boot as described here. After EFI install in VBox then the installed system boots normally.
Then on older notebook ASUS X550C (i5 3337U) I check ISOs:
x86_64 Plasma Rolling # 480 and Cooker # 478
and they both boot Legacy and UEFI. When I do this check I also check that intenet is connected or connect to wifi depending of the box I’m working on. Then check that Calamares installer opens and navigates to the partitioning page and check that all drives and partitions are recognized. Then open a few things at random from systray, app menu or desktop to spot check that things are generally working.
So on every box I normally test on here the ISOs (and the Calamares installer) are working OK.
Note: I also installed all 4 ISOs in VBox on my desktop (EFI boot).