Release notes:
https://www.freebsd.org/releases/13.0R/relnotes/Note able changes that are related to POWER:
POWER
All powerpc architectures switched to LLVM and are currently mostly similar to amd64 toolchain-wise. 678da4a27447
powerpc (32-bit) switched to Secure-PLT. e861dab45186
powerpc64le (64-bit little endian port) was introduced, targeting POWER8 and newer processors. b75abea4d087
Radix MMU support for powerpc64 and powerpc64le (experimental, disabled by default). 65bbba25d214
Superpages support for powerpc64 and powerpc64le (experimental, disabled by default). e2d6c417e303
LinuxKPI support. 937a05ba81c3
Support QEMU/KVM pseries without hugepages. b934fc74683b
Support for handling kernel minidumps. d3c34fc0f473
Optimized memcpy, memmove, bcopy, strncpy and strcpy. e16c18650cdc, 181e35008cfb, 075fb85f0904
XIVE interrupt controller driver for POWER9, which improves performance by about 10%. d49fc192c141
Converting pmap drivers to ifunc improved performance by about 20%. 45b69dd63
Plenty of stability fixes, which fix many kernel panics.
Plenty of other performance improvements - performance during bulk -a package building is at least 60% higher.