Help to remove a specific part of the background

[Necta]

Hi ! Sorry if i'm in the wrong section, i'm new here ! Please tell me if so.

So here's my issue. I've tried for days to remove the bottom right background of the main action bar.
See below => https://imgur.com/a/bV94KV5

I know it's possible because i saw a streamer having this part removed ( see image above ) .

Ideally i'd like to use my own script to remove it ( is it doable with a simple script tho ? ) so naturally i tried the command /FSTACK to find the element but i couldnt manage to get my hands on it.

I would be so gratefull if someone had an idea on how to remove it. A glimpse of a script maybe ?

Thx for reading me and sorry for my non native English ^^.