this worked. the phone is now running the open source treble OS, android 12.
i did not have to change the secure boot partition. - unlock the phone using mtkclient da seccfg unlock [link for details a couple posts back] - reboot into fastbootd, the graphical fastboot, and flash the system image with arm32_binder64-ab seems quite likely one could pull fastbootd out of the mix. and other things, some day.
