The culture is the same everywhere, any sex/gender, even in with internet streamers. Selena Gomez got death threats for her relationship with Justin Beiber back then. The difference is that the JP and KR industry knows better than to FAFO. Even female streamers are wary about the fans of male streamers in Japan.
It's not the same tho. The majority of Selena and Justin fans were fine with them dating, the only ones that had an issue were parasocial fans or people who generally didn't think they were a good fit for each other
With idols it's basically like 70-90% of Idol fans want idols to stay single
Also japanese female streamers are basically a subculture of idol culture, particularly vtubers. Well really any female streamer even the western ones are somewhat wary of showing boyfriends on stream because their viewership and donations drop, this is normal. That's why they keep it a secret unless them being in a relationship is part of the shtick like the ones who are dating other famous streamers.