Have successfully set the Apple JP keyboard keys for Japanese input switching work as they do on macOS. I’m nearly to the point where, while some things look slightly different (such as launchpad vs Whisker), the workflow is identical in both macOS and in XFCE with my modifications.
I’ve started a not-for-profit org called Mac Kimi (kimi is Japanese for “you”) in order to start getting older donated and repaired MacBooks into the hands of those in need. With these modifications, it should mean that the recipients (mostly children/teens) will have an Apple device which will allow them to transition to actual macOS on a newer device or on school/work devices and not stick out too much with their peers–they’ll have a MacBook with a visually appropriate, secure and up-to-date OS.
EDIT: now with an answer to Mission Control set to F3!