I'm Asian and have gone down this rabbit hole of research before, so here's some fun facts.
Thongs were extremely uncommon for women to wear throughout Japanese history. If anything, men actually wore them more (called fundoshis), though women wore them at times, but they mostly wore variations of shorts or long underwear. After World War II, "western" underwear like boxers for men and panties or thongs for women were integrated into society, somewhat similar in Korea as well (and now especially with the rise of Kpop in the west). Fun fact: some people attribute the popularity of upskirt photography in Japan to women not closing their legs in public after World War II, exposing their new "western" panties, because they were so used to wearing shorts or other underwear underneath skirts as women had done for hundreds of years. The panties were seen as scandalous and enticing at the time, as Japanese clothing had always been very conservative. This is just a theory, though, no hard evidence.
It's slowly getting more and more common I believe, not sure about China, but I think so in Hong Kong due to more outside influence. Otherwise, yes, thongs aren't that common across Asia, probably because they're so "new" (thongs as we know now have really only been worn since like the 80s/90s), while many Asian countries are thousands of years old. However, there are some outliers, I believe. For whatever reason they are somewhat common in the Philippines. I've seen many Filipino tiktoks advertising thongs (mostly for workout wear), and my Filipino girlfriend said her aunt wears them all the time, though there are still taboos about them there. Overall, in countries that are seeing thongs become more common (mostly in East Asia), there are still taboos surrounding them, as many view them as scandalous, slutty, western underwear.
As mentioned above, asian women in western countries are more likely to wear them, maybe less so they are first generation immigrants. For example, my girlfriend never wore thongs until I introduced them to her because her mom always told her they were too scandalous, though she seems fine with her wearing them now. I grew up around a lot of Japanese people, and throughout elementary and middle school in the 2000s, I remember seeing multiple Japanese moms with whaletails (although I didn't know what they were at the time, I just thought they had a wedgie).
I'm curious about western asia and the middle east, as I'm not very familiar with cultural norms there, and in many Islamic countries the women are covered up, so there's no chance for whaletails. I saw one guy online say that pretty much every girl wears thongs in the Middle East, but maybe he was just saying that.