[Google Pixel 5a] bulletfodder:
Mind sharing your steps?

I've downloaded the Sept update (full image)

extracted boot.img

patched with magisk

flashed to boot_a via adb

Checking the system page still shows June update.

Tried uninstalling Magisk, and I still can't apply the OTA.

Tried flashing stock (unpatched) boot.img, still can't apply the OTA.

Thankfully, I've made a full backup, so if I need to apply the entire image restore, I should be able to restore everything I need to. I'd like to avoid this. I want upgrading with root to not be a giant pain.

edit: process so far.

Download Sept update

edit the "-w" from the flash-all.bat

extract boot.img

send to phone

patch with magisk

pull to computer

reboot to fastbootd

run flash-all.bat

target reported max download size of 268435456 bytes
sending 'bootloader' (8754 KB)...
OKAY [ 0.035s]
writing 'bootloader'...
FAILED (remote: No such file or directory)
finished. total time: 0.043s
rebooting into bootloader...
OKAY [ 0.003s]
finished. total time: 0.005s
< waiting for device >
target reported max download size of 268435456 bytes
sending 'radio' (149780 KB)...
OKAY [ 0.685s]
writing 'radio'...
(bootloader) Flashing Pack version SSD:g7250-00132-210427-B-7316661
(bootloader) Flashing partition modem_a
OKAY [ 0.540s]
finished. total time: 1.227s
rebooting into bootloader...
OKAY [ 0.050s]
finished. total time: 0.051s
target reported max download size of 268435456 bytes
archive does not contain 'boot.sig'
archive does not contain 'recovery.img'
archive does not contain 'system.sig'
archive does not contain 'vendor.sig'
--------------------------------------------
Bootloader Version...: b9-0.4-7265224
Baseband Version.....: g7250-00132-210427-B-7316661
Serial Number........: 17211JECB****
--------------------------------------------
checking product...
OKAY [ 0.070s]
checking version-bootloader...
OKAY [ 0.069s]
checking version-baseband...
OKAY [ 0.069s]
sending 'boot' (98304 KB)...
OKAY [ 0.409s]
writing 'boot'...
FAILED (remote: Failed to write to partition Not Found)
finished. total time: 0.933s
Press any key to exit...

fastboot flash bootloader bootloader-barbet-b9-0.4-7265224.img

OKAY [ 0.144s]
writing 'bootloader'...
(bootloader) Flashing Pack version b9-0.4-7265224
(bootloader) Flashing partition table for Lun = 0
(bootloader) Flashing partition table for Lun = 1
(bootloader) Flashing partition table for Lun = 2
(bootloader) Flashing partition table for Lun = 4
(bootloader) Flashing partition table for Lun = 5
(bootloader) Flashing partition xbl_a
(bootloader) Flashing partition xbl_config_a
(bootloader) Flashing partition aop_a
(bootloader) Flashing partition tz_a
(bootloader) Flashing partition hyp_a
(bootloader) Flashing partition abl_a
(bootloader) Flashing partition keymaster_a
(bootloader) Flashing partition devcfg_a
(bootloader) Flashing partition qupfw_a
(bootloader) Flashing partition uefisecapp_a
(bootloader) Flashing partition featenabler_a
(bootloader) Flashing partition logfs
OKAY [ 0.601s]

fastboot flash boot "patched.img" and I get

sending 'boot' (98304 KB)...
OKAY [ 0.373s]
writing 'boot'...
FAILED (remote: Failed to write to partition Not Found)

Continue to flash to boot_a & boot_b

PS E:\8. Phone Backups\Pixel 5a\barbet-rd2a.210905.003> fastboot flash boot_a .\patched.img
target reported max download size of 268435456 bytes
sending 'boot_a' (98304 KB)...
OKAY [ 0.373s]
writing 'boot_a'...
OKAY [ 0.377s]
finished. total time: 0.752s
PS E:\8. Phone Backups\Pixel 5a\barbet-rd2a.210905.003> fastboot flash boot_b .\patched.img
target reported max download size of 268435456 bytes
sending 'boot_b' (98304 KB)...
OKAY [ 0.374s]
writing 'boot_b'...
OKAY [ 0.380s]
finished. total time: 0.756s
PS E:\8. Phone Backups\Pixel 5a\barbet-rd2a.210905.003> fastboot reboot
rebooting...

When I reboot, I'm still showing June Security update

Any thoughts?