12.3 live on a UEGI/GPT system

No - because there is no live CD.

There’s a live image, which you can put on a DVD or a USB. But it is too big for a CD.

The live USB, for 12.3 RC2 does boot in UEFI mode, though I did not try a UEFI install. I expect that the live image for 12.3 final will also boot into UEFI mode.