Android Verified Boot and generation of vbmeta image
In this page there is a section called 'Disabling verified boot' that mentions a commands to create an empty vbmeta.img that can be used to disable verified boot : https://wiki.postmarketos.org/wiki/Android_Verified_Boot_(AVB)

That command is,

$ avbtool make_vbmeta_image --flags 2 --padding_size 4096 --output vbmeta_disabled.img


To ensure this, I searched for 'make_vbmeta_image' in AOSP repositories and found a similar command in here.

I have an Android Q AOSP source tree with me. So I used avbtool from it to create an empty vbmeta image by issuing following commands.

$ cd &lt;aosp_root_dir&gt;
$ ./external/avb/avbtool make_vbmeta_image --flag 2 --padding_size 4096 --output ./vbmeta_disabled.img
$ ls -l ./vbmeta_disabled.img


As instructed here, to flash vbmeta image you can first boot your device to fastboot mode, unlock device's bootloader, and use following command.

$ fastboot --disable-verification flash vbmeta vbmeta_disabled.img