You could compile Python using the --without-threads configure option, before Python 3.7 [1] or thereabouts.
[1] 3.7.0 is the first major release following the removal of the config option in https://github.com/python/cpython/issues/75551 .. there's also a 2021 comment about "This has unfortunately turned out to be a blocker on getting WASI support as there's not direct threading support in WebAssembly."
[1] 3.7.0 is the first major release following the removal of the config option in https://github.com/python/cpython/issues/75551 .. there's also a 2021 comment about "This has unfortunately turned out to be a blocker on getting WASI support as there's not direct threading support in WebAssembly."