What is it?

You can use Smokeless_UMAF to configure almost all options on AMD systems including UMA Buffer size (For systems like the steamdeck and laptops), RAM overclocking, CPU power states and voltage settings, and much more, even if your system's BIOS doesn't expose the option for you.

Tutorial for increasing your UMA buffer on an AMD Phoenix Laptop

Boot into a FAT32 drive with the downloaded Zip extracted to the root, and then use the "Device Manager" section to locate the UMA buffer size.

The location within the utility is at

Device Manager > AMD CBS > NBIO Common Options.

Once set, back out and apply the changes, rebooting your system. You can then confirm that the option has been applied by checking your system monitor of choice (Windows > Task Manager, Linux > Whatever) and checking to see if your available RAM has decreased (indicating greater allocation of memory to the iGPU).

This may not remain applied through BIOS updates, and may cause hardware damage if misconfigured, and may result in an unbootable system if misused or by chance. You may need to reset your BIOS if that's the case, if possible by your system manufacturer.