I think this is the most up to date.<p><a href="https://www.interdb.jp/pg/" rel="nofollow">https://www.interdb.jp/pg/</a><p>Different author but also very interesting.
They keep publishing Russian version of this book, with the latest covering PostgreSQL 18: <a href="https://edu.postgrespro.ru/postgresql_internals-18.pdf" rel="nofollow">https://edu.postgrespro.ru/postgresql_internals-18.pdf</a><p>AI should do a decent job translating it to English.
To your point, PG15 has a pretty meaningful change to its base backup protocol<p><a href="https://github.com/wal-g/wal-g/issues/1385" rel="nofollow">https://github.com/wal-g/wal-g/issues/1385</a>