I can't select the acceleration option and it is stuck with software only. It's my first time encountering this problem. Any help would be appreciated.
Have you ever updated the graphics driver? Premiere Pro is very picky about the age of the graphics driver that's installed in your system.
Also, it may be that your integrated (not discrete) Radeon Vega graphics does not have enough processing units to enable GPU acceleration at all. Plus, Premiere Pro historically performs relatively poorly on anything that's equipped with even a discrete AMD GPU (where there are issues between Adobe's implementation of OpenCL support and that of AMD).
Worst of all, you will not be able to use hardware encoding at all because to my knowledge none of AMD's APUs have a hardware H.264/HEVC encoder at all.