I haven't used Windows scripting for a few years, but let's try to jog my memory and do something useful.

Since Windows does not have the file command, the best implementation of your pseudo code I can think of would be this:

for /f "delims=" %%A in ('where python ^| findstr /n . ^| findstr ^^1:') do (
  if /i "%%~xA" == ".exe" (
    set python_is_exe=true
  ) else (
    set python_is_exe=false
  )
)

findstr /n . will convert this

C:\Users\Aleksandar\.pyenv\pyenv-win\shims\python
C:\Users\Aleksandar\.pyenv\pyenv-win\shims\python.bat
C:\Users\Aleksandar\AppData\Local\Microsoft\WindowsApps\python.exe

into

1:C:\Users\Aleksandar\.pyenv\pyenv-win\shims\python
2:C:\Users\Aleksandar\.pyenv\pyenv-win\shims\python.bat
3:C:\Users\Aleksandar\AppData\Local\Microsoft\WindowsApps\python.exe

findstr ^^1: will get the first line from there

1:C:\Users\Aleksandar\.pyenv\pyenv-win\shims\python

%%~xA will get the extension

so it will be an empty string in this example, but if the last one were first, it would be .exe

I tested if this works correctly by changing 1: to 3: and restoring it to 1: again.

If anyone has a better suggestion than this, please share your idea.

With that code as a base, we can probably do something like this:

Instead of

if not defined PYTHON (set PYTHON=python)

we can just use

if not defined PYTHON (
  for /f "delims=" %%A in ('where python ^| findstr /n . ^| findstr ^^1:') do (
    if /i "%%~xA" == ".exe" (
      set PYTHON=python
    ) else (
      set PYTHON=call python
    )
  )
)

EDIT: I forgot to mention that this eliminates the need for other changes and that the remaining code can stay as it is. There is no need to use calls all over the script this way.