I am making this post because I feel that this information is not easily available. The ATmega328p-au is one of the most popular microcontrollers out there, and with these recent supply chain shortages, purchasing them has become extremely difficult.
I have noticed many of these "ATMEGA328p U-KR" chips and were totally miffed by what they were. I would go to purchase atmega328p-au's and when I asked for a picture I received pictures of chips labeled as "U-KR" or "U-TH". Finally, after hours of digging, a man on Alibaba has saved me. Apparently, these chips are the EXACT SAME as the ATMEGA328p-au; 0 differences except that they have a "new silkscreen". The "U-KR" part is just the location it was made, ie Korea (KR) or Thailand (TH). So for anyone worrying about not being able to use these chips because they aren't "P-AU" chips, don't worry, they are!
This is dumb I know, but now I know and so does everyone who is reading this. Also sorry if this is redundant, but I literally can't find this information anywhere else.