I was having this issue recently but I found a solution for it. The solution is to delete / rename the “Saved” folder in the UE5 project, this folder contains saved Graphic settings in addition to your own game’s save information.
If your game / project contains save data that is unique, this is where it is stored for your project. So be careful with it.
Once I did that I was able to overwrite the Editor scalability settings correctly. Before that it kept resetting to some medium settings.
I’m guessing this issue will happen again when any type of Graphic Option blueprints like a main menu forcibly save those settings to the disk.
You’ll just need to remember to reset or clear your game save in the Saved folder.