Well, a 5-year-old chip may not count as "recent" but the RK-3588 boot chain is "almost fully open-source" [1]. And it seems like it took a major amount of effort (from Collabora, others) to get it this far. I don't know of any equivalent or newer chips that are "more" open, but would love to hear if there are.
[1] https://www.collabora.com/news-and-blog/blog/2024/02/21/almo...