The ability to have"Disable top bar stickiness" unchecked and "Hide left navigation" checked is a wonderful feature. It keeps things similar to the way they are now.
With all the space freed up we have room to bring back the Rep to the top bar's avatar. This currently doesn't work for mobile devices with a high pixel density. On my Galaxy S9 with a reported resolution of 2768x1440, I see this in Firefox Mobile:
A possible workaround for large tablets - probably not desirable for a mobile phone:
Go to Settings and set your Font size to huge.
Go to "Developer Options", or use the 'Search Bar' and type "minimum".
Set the "Minimum Width" to 980.
The result on a mobile phone is difficult to use; but the StackExchange site shows your Avatar, Reputation, and Badges (the same as a few months ago).
On a large tablet it might be OK (untested) but on a phone the keyboard is especially tiny (could probably adjust that in the APP) and other APPs may appear different.
The phone's UI doesn't expect this and things are tiny with incorrect spacing. Many things don't look very good, I set it back the way it was and will simply visit my SE Profile if I'm curious while we wait for this to be fixed. Probably not useful on a phone, someone whom is eagle eyed might prefer this.
I thought I'd mention this in case it helps someone.
Here's a screenshot of what it looks like, and the Setting screens:
