I tried the same stuff as nedbat on WSL2, and I see similar change in the path of sys._base_executable (though I get a different "base" path on a3, so the path exists even there).

$ ~/.pyenv/versions/3.11.0a2/bin/python -m venv venv_a2
$ ~/.pyenv/versions/3.11.0a3/bin/python -m venv venv_a3
$ venv_a2/bin/python -c "import sys,os.path; print(e := sys._base_executable); print(os.path.exists(e))"
/home/ss/venv_a2/bin/python
True

$ venv_a3/bin/python -c "import sys,os.path; print(e := sys._base_executable); print(os.path.exists(e))"
/home/ss/.pyenv/versions/3.11.0a3/bin/python
True

$ cat venv_a2/pyvenv.cfg
home = /home/ss/.pyenv/versions/3.11.0a2/bin
include-system-site-packages = false
version = 3.11.0

$ cat venv_a3/pyvenv.cfg
home = /home/ss/.pyenv/versions/3.11.0a3/bin
include-system-site-packages = false
version = 3.11.0