Hello @Ahelion !
Please refer to ANDROID_USERS_GUIDE in chapter 5 (Programming Images).
There is explained the different methods for to download the images to SD card in your case.

There is a tool called imx-sdcard-partition.sh and it is used for download all images to the SD card.
Normally the use of imx-sdcard-partition.sh is:
$ sudo ${MY_ANDROID}/device/nxp/common/tools/imx-sdcard-partition.sh -f
<soc_name> /dev/sdX
# <soc_name> can be imx8mm,imx8mn,imx8mp,imx8mq, imx8ulp, imx8qm,imx8qxp.
and where sdX is the disk index assigned for your Linux host to your SDcard.
You can know what index is assigned to your SDcard with:
$ lsblk -t
I hope this can helps to you.
Best regards!