I got an update today. I asked the Thai Royal Embassy in Jakarta, and they said it’s fine to just write “Japan” for the country name. So, for Jakarta, it seems acceptable to write only the country’s name. They also mentioned that if there is a specific issue name stated in your passport, you can include that as well.

However, I strongly recommend asking the Thai Royal Embassy in the location where you’re applying. It seems that each embassy may have its own rules.