Sorry I don't get this. Now suddenly we talk about "old phones"?
The OnePlus 6 is not even listed on their, but also it states:
This list will be continuously updated as we learn of new devices updated, both officially and unofficially, with Treble support. This list will not cover every single device that supports Treble—that would make this list too long since Google requires every Certified Android device launching with Android 8.0 Oreo and above to support Treble.
Which means, every phone coming with Androud 8.0 or higher should support this by default.
So I really don't understand what you're trying to say.
and what has lineage to do with that all? O_o
You're talking about Phones not having software support, and then point out software projects, that are either not even related to any specific vendor, or are required by Google policy by default.
I really don't understand what you're trying to say nor what this has to do with (vendor) software support.