I'd guess Vega generation. As for lowest specs, it would be 12/14nm based, which is harder to find, so maybe not cheapest (eg. 200ge 3000g 3200g). So for commonly available parts, we're looking at the 7nm generation APUs (also Vega iGPU) 4600g, 5600g, etc, which on sale retail at around $100 shipped and are vastly superior to say the 3000g at a tiny premium. The latter come with quite good graphics, (roughly, 1080p low / 720p high gaming). Next step up in graphics would be the Navi generation 6400 RX Radeon card, which on sale can be had for $150, and likely at least doubles the graphics compute power compared to the 4600g/5600g APUs.
Comparing the lowest end offering (3000g APU) graphics versus the highest end among the budget tier mentioned above, the 6400 RX dedicated graphics card, it's 3X early generation Vega cores versus 12X second generation Navi cores. Furthermore, the 6400 RX's Navi cores run at ~ twice the frequency of the 3000g's Vega cores, so you have about an order of magnitude performance difference (over 8x) on the pricier option.
The 6400 RX has a beefier sibling, which uses the same silicon (though in a higher quality bin) run at twice the power budget (wattage) and with the full number (16X) of Navi cores active; it gets almost 2X the performance as its little sibling. It's called the 6500 XT and comes at a small price premium ($10-$20) over the 6400.
Some overview comparison reading:
https://www.cpu-world.com/Compare_CPUs/AMD_100-000000147,AMD_100-000000252,AMD_YD3000C6M2OFH/
https://www.techpowerup.com/gpu-specs/radeon-rx-6400.c3813
