Asklemmy

I can't speak for Hinduism, but this Wikipedia article goes into some of the history of Buddhism in regards to sexuality. Generally, sex of all kinds, whether heterosexual or homosexual or sex with celestial beings, was seen as another one of the 10,000 things that could distract one from the path - but otherwise there was nothing particularly immoral about it. Monks and nuns generally had to follow rules that prohibited both, in order to remove distractions, but those rules were never meant for the general public, aside from the precept against the "misuse" of sexuality, which is ambiguous but thought to refer more to things like SA.

When we're talking about modern China, or the present day state of other historically Buddhist countries, it would be reductive to say that their current attitudes towards homosexuality are a product of religion, because it ignores more recent events and currents, and other historical factors. China was also historically influenced by Confucianism, which was more homophobic, but it was also influenced by a bunch of other philosophies, and today it's not very religious at all. Japan was historically very gay, and the 11th century Tale of Genji has a bisexual protagonist fucking everybody.

However, every historical tradition had to adapt to contact with the West during the age of colonialism. China at first tried hard to cling to its traditions and stubbornly refuse to adapt to new, Western ideas, but the "century of humiliation" happened and they realized they had to adapt or die. Japan was not directly colonized, but they still had a massive revamping of their society with all these new ideas coming in. Every country in Asia has a story like that. And then you have another 100 years of stuff happening after that.

China's modern day homophobia does not come from a place of "The Buddha said this was bad," rather, it comes from seeing homosexuality as a Western invention, and a symptom of "bourgeois decadence." Sadly, such brainworms are common in many socialist countries. There is a stereotype many people have that gay people all live in cities and spend all our time partying at nightclubs, because that makes for better TV than the reality does. Ironically, there are many countries in the world that once had their own more tolerant traditions that were replaced with Western values during colonialism, who now hold those values up as their own against more progressive, modern day Western values.