On Macs, you can set up your language keyboard to toggle between various Japanese input methods and keyboards in the same "set":
In my case, with this, I can hit the "switch keyboard layout" section and toggle between a US, French, then "US/Hiragana IME"/"US/Katanana IME", etc.
When I just set up the (I believe) ibus-mozc
IME for Ubuntu in Gnome, when typing in Japanese I have to first switch to the "Japanese (Mozc)" layout, then use some Mozc-only key command to switch input methods.
Is there a way to instead make the IME methods first class? I am fine switching IME setups entirely, but this is a constant source of frustration for me given the keyboard layouts I use.