Did you install the Python mode? Here’s what I see on my system when I click on the mode box in the upper right hand corner of the editor:
I just now noticed that the Modes tab is empty on my system too. No wonder you can’t install it! Perhaps it got lost on the last update. I’m using version 4.1.1.
Addendum:
I just switched to a Windows 11 system and was able to install the Python mode (now shows up in menu) using the technique described in @jafal 's post. I extracted the .zip file (in Downloads folder) into c:\Users\myName\Documents\Processing\modes and it worked.