[Essential Phone Questions & Answers] noideawtf:
Here is the sequence of commands:

C:\Users\blah\Desktop\platform-tools>adb devices

* daemon not running; starting now at tcp:5037

* daemon started successfully

List of devices attached

PM1LHMA7blahblah unauthorized

C:\Users\blah\Desktop\platform-tools>adb devices

List of devices attached

PM1LHMA7blahblah device

C:\Users\blah\Desktop\platform-tools>adb reboot bootloader

C:\Users\blah\Desktop\platform-tools>fastboot devices

PM1LHMA7blahblah fastboot

C:\Users\blah\Desktop\platform-tools>fastboot getvar current-slot

current-slot: _a

Finished. Total time: 0.001s

C:\Users\blah\Desktop\platform-tools>fastboot flash vendor_a vendor-QQ1A.200105.088.img # OOPS i should have put b so i try to fix it in the next command

Sending 'vendor_a' (392296 KB) OKAY [ 9.211s]

Writing 'vendor_a' OKAY [ 2.446s]

Finished. Total time: 11.667s

C:\Users\blah\Desktop\platform-tools>fastboot flash vendor_b vendor-QQ1A.200105.088.img

Sending 'vendor_b' (392296 KB) OKAY [ 9.215s]

Writing 'vendor_b' OKAY [ 2.439s]

Finished. Total time: 11.661s

C:\Users\blah\Desktop\platform-tools>fastboot erase system_b

Erasing 'system_b' OKAY [104.577s]

Finished. Total time: 104.580s

C:\Users\blah\Desktop\platform-tools>fastboot flash system_b system.img

Invalid sparse file format at header magic

Sending sparse 'system_b' 1/6 (523151 KB) OKAY [ 12.365s]

Writing 'system_b' OKAY [ 3.943s]

Sending sparse 'system_b' 2/6 (520769 KB) OKAY [ 12.262s]

Writing 'system_b' OKAY [ 3.271s]

Sending sparse 'system_b' 3/6 (523599 KB) OKAY [ 12.327s]

Writing 'system_b' OKAY [ 3.311s]

Sending sparse 'system_b' 4/6 (522306 KB) OKAY [ 12.262s]

Writing 'system_b' OKAY [ 3.563s]

Sending sparse 'system_b' 5/6 (503327 KB) OKAY [ 11.967s]

Writing 'system_b' OKAY [ 8.774s]

Sending sparse 'system_b' 6/6 (42300 KB) OKAY [ 1.068s]

Writing 'system_b' OKAY [ 0.311s]

Finished. Total time: 87.248s

C:\Users\blah\Desktop\platform-tools>fastboot flash boot_b unsigned-new.img

fastboot: error: Couldn't parse partition size '0x'.

C:\Users\blah\Desktop\platform-tools>fastboot flash boot_a unsigned-new.img

fastboot: error: Couldn't parse partition size '0x'.

C:\Users\blah\Desktop\platform-tools>fastboot flash:raw boot_b unsigned-new.img

Sending 'boot_b' (23864 KB) OKAY [ 0.634s]

Writing 'boot_b' OKAY [ 0.298s]

Finished. Total time: 0.958s

##FORGET TO USE COMMAND fastboot set_active a

C:\Users\blah\Desktop\platform-tools>fastboot -w

Erasing 'userdata' OKAY [ 54.443s]

mke2fs 1.45.4 (23-Sep-2019)

Creating filesystem with 26768215 4k blocks and 6692864 inodes

Filesystem UUID: blah

Superblock backups stored on blocks:

32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208,

4096000, 7962624, 11239424, 20480000, 23887872

Allocating group tables: done

Writing inode tables: done

Creating journal (131072 blocks): done

Writing superblocks and filesystem accounting information: done

Sending 'userdata' (544 KB) OKAY [ 0.100s]

Writing 'userdata' OKAY [ 0.018s]

Finished. Total time: 54.827s

Now when i restart the phone it just stays on the screen with the essential logo and powered by android at the bottom; never gets to spinning circles. When I restart i can pause it from booting because the bootloader is unlocked, but adb cant find it because to do that i have to give it debug permissions, but no OS to boot to so i cant do that. Did i brick my phone?