LED artifacts 128x128

[gadjodilo83]

Hello

I'm using a Raspberry Pi 5 with four 64x64 (128x128) LED arrays. When the brightness is greater than 0.5, I get individual lines that flicker occasionally. I use the following script: virtualdisplay.py

Basically, I followed the following tutorial: https://learn.adafruit.com/led-matrix-wall-arcade/

Is this a known issue, and is there a way to fix it?
Since I'm using darkened acrylic, I need a brightness greater than 0.5, otherwise the LEDs would be much too dim. Is the Raspberry Pi 4 a better choice, since I've read that it supports PWM.

Thanks
Marc