On Windows:
You can create a shortcut executing
Anaconda3\pythonw.exe Anaconda3\cwp.py Anaconda3\envs\<your_env> Anaconda3\envs\<your env>\pythonw.exe Anaconda3\envs\<your_env>\Scripts\spyder-script.py
However, if you started spyder from your venv inside Anaconda shell, it creates this shortcut for you automatically in the Windows menu. The steps:
install spyder in your venv using the methods mentioned in the other answers here.
(in anaconda:) activate testenv
Look up the windows menu "recently added" or just search for "spyder" in the windows menu, find spyder (testenv)
and
[add that to taskbar] and / or
[look up the file source location] and copy that to your desktop, e.g. from C:\Users\USER\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\Anaconda3 (64-bit)
, where the spyder links for any of my environments can be found.
Now you can directly start spyder from a shortcut without the need to open anaconda prompt.