Hardware Encoding unavailable for 4K (Level 5.2) Export - Premiere Pro

I've just bought a brand new 16in Macbook Pro 2019 model (purchased in July 2020).

2.3 GHz 8-Core Intel Core i9

32 GB 2667 MHz DDR4 RAM

AMD Radeon Pro 5500M 8 GB Graphics Card.

I'm using the latest version of Premiere Pro 14.3.0 and want to export my 4K (3840x2160) timeline as a h.264 file.

I realise it won't let me use Hardware Encoding during export settings when the level is set to 5.2, but when I set it to 5.1 or below (which is not large enough for 4K resolution), hardware encoding becomes available. I have it set to VBR 1 pass also.

Is this just an issue with the software, because my computer hardware specs should be more than enough to handle 4K Hardware Encoding exports.

Anyone else trying to export 4K resolution with Hardware Encoding and having this problem?

Thank you.