Linux kernel 5.12 changelog.
Other new sources:
LWN's merge window [https://lwn.net/Articles/847057/|part 1], [https://lwn.net/Articles/847451/|part2]
Phoronix Linux 5.12 [https://www.phoronix.com/scan.php?page=article&item=linux-512-features&num=1|Feature overview]
Or take instead a look at the list of Pull Requests:
