Thanks to @Yahoo Mike
we now have a working TWRP for A13 GSI ROMS, decryption is working and even backup and restore.. you guys are welcome to try it in your devices, it will allow you to root the easy way and install future magisk updates since direct install does not work because of /dev/block/mmcblk0p28 being read only, so for now the only way to update it will be through TWRP which is a game changer already, otherwise the only other way was to patch the boot.img every time and flashing it using fastboot which was a pain in the ass and always required a computer. Attached is the TWRP test img, as I said you guys are welcome to test it so that Mike can go ahead a release it.
1: Restart to bootloader from the restart menu or by using command adb reboot bootloader
2: fastboot flash recovery twrp_X606FA_12.1.fbe.img
3: fastboot --disable-verification flash vbmeta vbmeta.img
4: fastboot reboot recovery (to go to recovery) or fastboot reboot (to reboot system)
5: (optional) but good for testing... flash something, you can flash the magisk APK that I attached on this post earlier, just decompress the zip and when in recovery you can just select the apk and it should flash.
Feedback would be great to make sure it works for you guys, everything on my end and Mike's end seems to be working good.