My time to shine again. First off, RZ is the top trim in Japan, so you got all the extras - 8 speakers, steering headlights, heated seats etc.
As for the head unit: That's the base 7inch Toyota navi unit that can be purchased as an optional extra when ordering cars here in Japan (all GR86 here come standard with NO headunit at all. You have to pay $$$ to have Toyota install one). The units are... fine? I guess? But for your purposes they're kinda useless. You'd be best off swapping something else, unless you can read Japanese. There's no way to switch languages, and AFAIK the maps/navigation will not work outside of Japan.
The good news is you can put in pretty much anything you want from here on. 7inch units will use that extra bezel piece surrounding the head unit, but you can remove that and install a 9inch unit which will look way cleaner.
You'll need to find a breakout adapter plug in order to connect aftermarket head units, so might need to do some research on what you can buy in your area. Here's a Japanese website with an example of the type of connector you need:
トヨタ GR86 TOYOTA GR86 (subaru BRZ) カーナビ取付けに必要なハーネス・カメラ変換・ステリモ変換 配線適合表 時風プレイス jifuplace. It's the first product in the list.
Given the previous owner installed a Toyota navi system, they might have also added the reverse camera. However In order to use that with other head units you'll need a converter to change it to an RCA (yellow video) plug. You can see that at the same link above, product name is: スバル純正バックカメラ. I think the product number is something you can search and maybe somewhere near you sells it.
Personally, I went with a 9inch Joying android unit. Ordered from Aliexpress. Used adapters from the website above.
Feel free to ask anything else. This is kinda my one area of expertise with these cars lol.