Weird Bios issue "B450M-HDV

I see quite a few people trying to manually set the UMA size. There is no need
to do so, the size is set as needed by the OS. On old motherboards with built in
graphics (the iGPU is on the CPU now) you used to have to set the shared memory
to a larger size in order to run certain games. Today however the system will automatically
assign memory to the iGPU depending on RAM available and the needs of the
application/ game being run. Forcing the size can cause instability and even
prevent some games from running as the maximum forced size is lower than the
amount the system is able to automatically allocate.

The setting exists to force lower RAM usage. Even this is largely pointless now
as the system will simply allocate less RAM when the it's needed elsewhere.
As a result, AMD has not put much effort into maintaining this feature and it
is often broken for various APU generations.

If you were to use a 1gb dedicated GPU and ran out of VRAM the system would allocate
system RAM in an attempt to compensate. System RAM is slower than VRAM on a
dedicated GPU so you end up with a drop in FPS or worse, poor frametimes/
stutter.
This is not a factor with an iGPU that uses system RAM all the time. There is
no difference in speed between the allocated RAM and the rest of the system RAM
and so there is no stutter/FPS drop when the system swaps from allocated RAM to
system RAM as needed.

I hope this is helpful.

The update should work fine with your setup, I just don't think it would be worth
updating. I suspect the update won't fix the issue, as I said, AMD has neglected
this feature, probably due to the limited value of it to the majority of it's users.

Check carefully though your BIOS, sometimes settings are duplicated in multiple
places and only one of them will work. I don't have your board so I can't check
for you. Good luck.