With phyBOARD-Pollux rev 1552.2 the enable GPIO for the LVDS1 on the baseboard is inverted and needs to be set to active low. If you want to connect a display via LVDS1 interface, you can fix the issue by applying the patch to meta-phytec. After applying the patch build the PD21.1.1 release:

./phyLinux init -p imx8mp -r PD-BSP-Yocto-FSL-i.MX8MP-PD21.1.1

"git am 0001-kernel-imx8mp-phyboard-pollux-Change-backlight-gpio-.patch" in sources/meta-phytec

The issue will be fixed in the upcoming PD21.1.2 release until End of October 2021.