Sorry, but I don’t understand why you bring up the exact same thread again. Your questions have already been answered as good as possible in the other thread.
in my humble opinion, these aren’t issues that Nextcloud can or should solve. Also, these issues are not specific to Japan, but rather to the web hosting provider / shared hosting plan you are using.
If you are still convinced that the Nextcloud developers should change anything in their .htaccess file, please open an issue on GitHub, and describe exactly what they should change and why: Issues · nextcloud/server · GitHub
This xserver company (unfortunately everything is in Japanese and I can’t find an english version) seems to provide VPS as well, that look more suited for Nextcloud: https://vps.xserver.ne.jp/
However, the price and the size of the storage, I’d rather start with a Raspberry Pi 4 at home. Not sure about the situation in Japan, they are supposed to have good fiber connections, so perhaps it’s a good option to host from home that way. And once you manage to make it work, you can easily grow to a more powerful device if needed.
That can be difficult, although most of us here have English as second language as well. We also have language-specific forums where you can ask, even in Japanese:
But it takes some time to build a community around a language and get answers in a short time. And you exclude users of different languages.