Ok, I'll do that now.
In the mean time I built a core-image-x11 for imx6qdlsabresd with following changes in local.conf:

DISTRO ?= "fslc-x11"

ACCEPT_FSL_EULA = "1"

IMX_DEFAULT_BSP = "nxp"

CORE_IMAGE_EXTRA_INSTALL += " \

    packagegroup-fsl-gstreamer1.0-full \

"

With none of my own layers enabled, and the problem persists.

root@imx6qdlsabresd:~# uname -an

Linux imx6qdlsabresd 5.4.70+g2d1241e38347 #1 SMP PREEMPT Wed Oct 7 17:10:48 UTC 2020 armv7l GNU/Linux

root@imx6qdlsabresd:~# DISPLAY=:0 gst-launch-1.0 videotestsrc ! imxeglvivsink

Setting pipeline to PAUSED ...

Xlib:  extension "XFree86-DRI" missing on display ":0".

Pipeline is PREROLLING ...

Xlib:  extension "XFree86-DRI" missing on display ":0".

Xlib:  extension "XFree86-DRI" missing on display ":0".

Pipeline is PREROLLED ...

Setting pipeline to PLAYING ...

New clock: GstSystemClock

Caught SIGSEGV

exec gdb failed: No such file or directory

Spinning.  Please run 'gdb gst-launch-1.0 474' to continue debugging, Ctrl-C to quit, or Ctrl-\ to dump core.