Just if someone else runs into this issue: for some reason (I don't know which) pressing Alt key and left mouse button does nothing in my Blender. Instead when I double click a vertex / edge / face in Edit mode I get the loop selection.
That's probably to do with your settings rather than a different version of Blender.
Or it could be because of a tool selection mode or even an add-on changing default behaviour.
It's hard to say exactly why without seeing it in Blender.
If you still have this issue, could you record a video, or add some images, of your Blender, showing the toolbar, the Keymap preferences and any add-ons you have enabled, and the action itself.
Video can be uploaded to google drive, dropbox or similar and share the link here
Images can be added via the image icon on the content toolbar.
Never heard of that behavior before, but now that I think about it it's blowing my mind, Blender has no double click functions and that's so computer basics. And somehow you double click and get loop selection? That is some October Halloween scary movie type of stuff. I'd try any of the solutions out just so you don't get accustomed to loop selecting like that and because it's freaky.
You are using emulate 3 button mouse. When you check that it makes face/edge loop select double click. This has been in blender since 2.76b.
Ah, thank you Dwayne dillenbata3 ,
(But that is only when also using Left Click Select. Because ALT+LMB becomes the MMB. If you use RCS, then Loop Select is ALT+RMB and that still works.)
I'm using 2.83 LTS and I can confirm that with "Emulate 3 Button Mouse" is turned on, double clicking Left Mouse Button = Loop Select.
With "Emulate 3 Button Mouse" turned off, ALT+ Left button mouse = Loop Select