Comment # 6 on bug 1190737 from Axel Braun

(In reply to Guillaume GARDET from comment #5)
> The log suggest a memory issue:
>   glamor: Failed to allocate 1920x1080 FBO due to GL_OUT_OF_MEMORY.
> 
> Could you try to increase GPU memory, please?
> This is in config.txt file. The default is gpu_mem=32
> You can try 64, 128, or 192.

I increased it up to 192, no change

all files of pattern xfce have already been installed

I tried setting 
dtoverlay=disable-vc4
resulting in the fact that the xserver did not start at all anymore