Speed Shift Max was designed and tested on my 10th Gen CPU which was before the E cores existed. I have never tested Speed Shift Max on any 12th Gen or newer CPU. As for as I know, Speed Shift Max can still be used to control the maximum speed of the P cores. I do not know how or if this ThrottleStop setting limits the speed of the E cores.
A Speed Shift Max setting of 50 used to be exactly equal to 5000 MHz and a setting of 40 was 4000 MHz., etc. On 12th Gen and newer CPUs this relationship no longer seems to be one to one. You should still be able to use Speed Shift Max to control the maximum speed of the P cores. Other users have confirmed this.
If you want to do some testing, run a consistent load like Cinebench. While Cinebench is running, vary the Speed Shift Max value and watch what MHz value ThrottleStop reports for the P and the E cores. Watch the Limit Reasons data while testing to make sure your CPU is not thermal throttling or power limit throttling.
It might be possible to edit the Windows power plan you are using so you can fully control both the P and the E cores. Without access to a computer running Windows 11 or any recent hardware for testing purposes, I have decided to leave the Speed Shift Max feature as is.