Which environment does '%%bash' cells run in Jupyter for Windows launched from base env via Anaconda Prompt (PowerShell)?

With !, you automatically execute code on the commandline (CMD). Therefore, you can run any commands that also run inside a CMD with it. For example, with !ECHO %%PATH%% you get whatever is in your current PATH variable. Whatever application you want to run, the directory with the application’s exe file must be listed here. You can also invoke a command that in turn invokes something else, e.g. !powershell Get-Command aws would show what PowerShell believes “aws” should resolve to - here most likely nothing. You might need to install a few commands and either clutter your PATH variable with them (with the danger of breaking your system if you accidentially redefine commands that already exist under Windows) or you fix all the Shell commands by invoking a Shell and passing your command to that Shell, similar to !C:/path/to/my/working/shell.exe <mycommand>.

Maybe an easier alternative could be to just run that Jupyter Notebook(s) inside a virtual machine with Linux. You might be interested in Hyper-V, VirtualBox, or maybe even WSL. Then you can run all the Shell commands natively on that OS.