Yes and no.
The change is to align the signing of the paritions to match OOS, but the result is that the bootloader still won't relock with a custom OS.
I've been working on this in my spare time, but no luck so far.
From what I've seen of the OOS 12 bootloader, it looks like they've made a lot of changes to it (aka replaced it with the one from OPPO). This may include removing the custom avb key support. If so, there's not much we can do
The OOS 11 abl partition was ~2m, where as the new OOS 12 abl parition is about 200k. OOS 13 beta abl parition is about 200k as well.
EDIT: Note this is only with reference to the Oneplus 9 phones, older phones like the 6/6t don't have newer versions of OOS so it's not an issue, you can still relock the bootloader using the existing guide with LineageOS 19.