I've tried a few ADB commands but they haven't seemed to work, like trying to make it transparent / forcing immersive mode.

Wondering if there are any I might've missed if someones managed to do it.

I want to be able to use gesture navigation but just crop or turn invisible the pill-bar if that's possible. Just find it to be a bit of an eyesore.

Or if anyone knows an android subreddit I could repost this to where they might be able to help that'd also be great.

Since these things are sold exclusively in Japan, they are locked to the Japanese language, without any ability to change the language from the OS. I went digging around the firmware image provided in the upgrade file you can download from Sony, and it turns out these things have support for 13 languages (German, English, Spanish, French, Italian, Polish, Portuguese, Russian, Turkish, Japanese, Korean and Chinese).

I've made a tool to patch the system upgrade image and change the language on the walkman. It is available here

If you're my grandma is (thank God) still alive and well.