Yoe maybe interested in the just ratified "RISC-V Bit-Manipulation ISA-extensions" https://github.com/riscv/riscv-bitmanip/releases/download/1....

There is some overlap. There's the "Zbkb" (horrible name, I know) extension which contains a subset of instructions from the larger bitmanip extensions which are very useful for cryptography.

The more general bitmanip extensions contain other things useful for e.g. address arithmetic. These are somewhat orthogonal to scalar crypto.