This app was mentioned in 2 comments, with an average of 1.00 upvote
Since you have Xposed, install this app from here. http://m.coolapk.com/apk/de.robv.android.xposed.mods.appsettings
You might be familiar with it, this version works with Android 6/M. Just click on the green button on the left with the download symbol.
There is an option to disable or force immersive mode.
If you wanna try something else, this app doesn't seem to require root. https://play.google.com/store/apps/details?id=jp.kshoji.statusbarkeeper
Personally since I am on Nougat (no Xposed for me) I just downgraded the app to an older version, the performance seems to be the same. Just remember to disable auto-updating in the Play Store.
Sure, I actually got two methods. The first one doesn't require root, but it's kind of an hit 'n miss.
1) Install this app from the Play Store, launch it and profit.
2) You not only need root, but also Xposed Framework, so this method is applicable only on Android 6 Marshmallow or older (not Nougat, not the upcoming Oreo). Once you have set up your systemless root and systemless Xposed, install a module Called App Settings. From there you can change lots of thing, and there's the option to forbid an app to use immersive mode.
Personally since I'm on Nougat 7.1 I can only use the first method. Another method would be editing the APK manifest but that will trigger DeNA's signature verification, just like it did when I tried to disable the FPS capping at half the refresh rate of the device (so we could basically get reliable 60 fps)