The Python cryptography library switched out C for Rust which invalidated some platforms[0]. 2021 story, so not sure if anything has changed.

   ...Since the Gentoo Portage package manager indirectly depends on cryptography, ""we will probably have to entirely drop support for architectures that are not supported by Rust"". He listed five architectures that are not supported by upstream Rust (alpha, hppa, ia64, m68k, and s390) and an additional five that are supported but do not have Gentoo Rust packages (mips, 32-bit ppc, sparc, s390x, and riscv).