The mseal() syscall was merged for #Linux 6.10: https://git.kernel.org/torvalds/c/0b32d436c015d5a88b3368405e3d8fe82f195a54
It's a way to prevent changes to portions of the virtual address space – and quite similar to #OpenBSD's mimmutable() syscall.
For details see the docs (https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/plain/Documentation/userspace-api/mseal.rst) or two @LWN articles (https://lwn.net/Articles/948129/ and https://lwn.net/Articles/958438/)