I had the issue where the editable/read only drop down was completely gone, none of the above worked for me.
For me, the reason that this broke was because for some reason Autodesk gave me the full version for free... for a limited time. if this was intentional I'm guessing it was so that they hope I will get used to the better features and want to come back when it expired. it happened randomly one day when I logged on and realized that the document limit was gone (I took as much advantage of it as I could for a time lol). however, the issue is that when that full version expires, Autodesk WILL NOT automatically roll you back to the free version that you were on before, you will be stuck on an expired license. You can tell if this happened to you by looking at the top left corner of your screen and seeing if it says "expired" somewhere on there.
You will need to go to your Autodesk account online and "re-download" the free/for personal use version. You (probably) don't have to actually run this installer, but now in their system system you have registered for a personal use license, instead of an expired full license, so now if you follow the other steps some people have mentioned (update, log out/log in, clear cache, etc.) one of those should get the editable/read only drop down back.