I made some changes to some of the material shaders and then saved it. Now I’m starting to regret these changes but I don’t exactly remember which shader I used before. So, is there a way to retrieve a previously saved scene?
Yes - using source control.
You could check the Temp folder and look for a folder called _Backupscenes, my understanding is that this is a backup that is created each time the play button has been pushed. I found this useful after I had accidentally saved over a completed scene that I had been working on for four days with an empty scene. I found a file named 0.backup in the folder and changed the .backup to .unity and was amazed to see my scene.