I just got the device (Pi 3 Model B+) and am a total beginner.
I'm using NOOB/Raspbian. Every time I try to change the video ram (either through the GUI or the config.txt) the device is unable to boot, it just flickers between a black screen and the screen turning off. Even when I revert the changes of the config.txt via recovery mode, the problem persists.
I reinstalled Raspian about 4 times already, and am about to do so again, but being able to change the amount of vRAM would be nice.
I used the OpenGL driver, which I changed through raspi-config. I tried to change the vRAM to a reasonable amount (128). The only software I installed was xscreensaver, gwenview and redshift (a blue light filter that auto starts.). I'm using the official 2.5A power supply.
Does anyone have an idea why this happens (even after I revert the changes in the config)? Could it be connected to the software I installed, or OpenGL?
[EDIT]: Solved. I was advised at the RasPi forums to get rid of NOOBS and just flash the SD card with Raspbian stretch. That solved all my problems and made the device boot 5x faster.