I can't find an answer even tho I have solved this issue already once. For some reason when I double click .blend file it opens it in 2.79 instead of 2.83. All I remember that there are multiple ways to set this in windows 10 but I can only remember one and that doesn't work. Which is to right click the .blend and set it to open with the 2.83. There is one thread about this from 2015 but it is useless nowadays. I can't delete the 2.79 as I need it for some files that I don't want to convert to 2.8+.
Seems like you encounter the dumbest design the windows registry system can potentially have. If the executable name is the same one (
.blend here), it will cause some bug and not updating the table correctly.
You can make your blender 2.79 executable named as
blend279.exe. This will let the register miss the original 2.79 exe and update the new value after choosing new blend file.
example below to make it "forget" 2.83 blender:
if it's not too much of a hassle, i'd uninstall blender 2.79, open the file, then direct it to blender 2.83, and then afterwards I'd download the portable version of blender 2.79 so you can just keep it as a folder on your desktop. That way, it will only open when you specifically go out to open it.