Never that popular in America and never heard anything about it's presence in Japan aside from maybe some studios using it?
I do know that Kanye West had an Amiga as he talked about it in an interview, but nothing Commodore did really had a big impact in America where the PC reigned supreme even when the capabilities of high-end PC's were pathetic compared to an Amiga.
People have debated over the reasons why the Amiga never found it's market outside of UK but not much that is concrete has been said aside from people perceiving the Amiga has just an expensive gaming machine and bad marketing campaigns in America where it sold less than a million units in it's commercial timeline.
It did sell close to 5 million but in it's years in the market, it sold at best 700,000 units in America, and even in Europe, the Amiga was much more popular in UK and Germany than the rest, though it was still a popular computer, just not to the same extent.
As for it's sales in Japan, seems to have been very few, but again, studios did use it, there are artists who used it, most of the soundtrack in the first few Pokemon games were apparently done on Amiga computers and then converted to the game's music format.
That being said, looking at an interview, it seems that Amigas weren't even sold in Japan usually, and when it launched, it seems Commodore only sent 10,000 units because even the Commodore 64 failed there, but the Amiga was such an amazing computer for art that artists and studios who heard about it bought it.
For example, in said interview, a guy mentions he can't even do a meeting between Amiga fans and apparently never had one even when the computer was on the market because it was that unknown and unpopular, with, again, only artists and studios using it.