If you’re learning Japanese, then “10ten” is very good. It adds a little “puck” you can use to hover over words and phrases to see their dictionary definitions, readings, etc.
(On desktop, it instead works whenever yoy hover your mouse cursor over a word, but on mobile, that’s not a thing. Either way, it’s easy to turn on/off based on your need.)
You can use notification settings to “Minimize” any unwanted permanent notifications – in that way they’ll not show an icon in the tray area. (You can also just disable any notification type, but Android is more likely to stop any background task that doesn’t display a notification.)