Hi guys,
I am currently using this asset to open a browser within Unity on iOS: In-App Web Browser | GUI Tools | Unity Asset Store
However, it is terribly laggy, so I’m wondering how I can do it myself in the most simple way possible to check out whether there’s less lag.
I’m also open to any advice on how to decrease lag.
Please note my “game” is an app that is purely GUI, but there might still be a way to decrease lag, I don’t know. Turn off rendering or something? Turn off cameras?
I’m open to advice, thanks. 
Note the browser works fine on Android.
Profile your build to see where the lag is coming from. It is not possible to tell you how to fix a laggy experience without that information. Otherwise contact the creator of that asset, as they may already be aware of the issue and have ideas for work arounds.