Many devices if you load up fastboot mode (is that the right name?) it will give you chipset and other information and it will have secureboot info there. It's permanently locked to chain into the AVB image. AVB is a much more complicated beast that specifies the existence of multiple partitions including (IIRC) one for storing authorized keys, one for the recovery, and a bunch of other stuff.

It's possible this has changed or was never widespread in the first place. I have a very limited (and historic) sample size.