It totally depends on if you run into the same issue. I guess there’s lots of potential for other bugs that lead to memory leaks, so there’s no guarantee that the CVar helps in your case.
For that CVar to actually work, it is important that you start the project with that CVar. Yes, you can set it at runtime, but the issue is only gone when you start the engine with that CVar. Setting it in the DefaultEngine.ini file is the correct way to do that.
Regarding UObjects increasing and decreasing, that should be another issue. That GPU collection feature is not bound to UObjects, but to a data structure like an array, as far as I can see in the code. Note that it’s quite normal for Unreal to seemingly randomly allocate memory for UObjects that pile up until the garbage collector decides to remove them and free memory. Depending on the project a change between 14GB and 22GB can be quite normal, especially if Unreal is doing something in the background, like preparing data for the DDC or loading stuff.