I installed Manjaro KDE 5.20.3 with Kernel 5.4.80 yesterday on a new SSD hard drive. Updated everything, and for the first time ran into an issue with installing the virtualbox extension pack 6.1.16. I installed the official repositories virtualbox-ext-vnc, version 6.1.16-1, and that did not worked. Kept telling me the wrong password.Then I installed it via Oracle’s virtual box website with the same result. Didn’t work. It kept telling me the wrong password no matter what I did. Then searching through the forum I installed the virtualbox-ext-oracle (AUR) version 6.1.16-1, and that worked. So everything is working now, but I’d like to know if this a bug with kernel 5.4.80-1 (LTS)? I like to use the official repositories over AUR as it’s less problematic!
Wrong password for what? The VNC server you don’t have? 
The Oracle Extension Pack is in the AUR because of the proprietary license, otherwise it would have already been in the Arch repos.
When you download the the virtualbox extension pack from Oracle’s website in your download folder, and execute it - you have read the disclosure and agree to the term. At that point it asks for your login user password, but it was telling me the wrong password.
I have downloaded the same “VirtualBox 6.1.16 Oracle VM VirtualBox Extension Pack” on at least 4 other computers without any issue, and I have always installed the vbox extension pack directly from Oracle’s website, but this time it was not working until I was forced to download it from pamac-AUR to make it work.
Forced to do what now? pamac is in the Manjaro repos, pamac-aur is in the AUR for Arch and other derivatives. Are you actually using Manjaro?
Let’s be clear: virtualbox-ext-vnc is in the Arch community repo and virtualbox-ext-oracle is in the AUR. The latter is what you need. They are two different things.
Yes, I realized after you mentioned I never needed the vbox-ext-vnc to begin with! How ever, you do need the “VirtualBox 6.1.16 Oracle VM VirtualBox Extension Pack” for Virtualbox to work. I have always downloaded the vbox extension pack from Oracle’s website in the past, and installed it. This time I was getting an authentication error when I was entering my user password after agreeing to the user term. So I found out from a previous post and installed it via Add/Remove Software under (AUR), and it worked.
You get this error if you try to download it directly from Oracle’s website:
Result Code:
Failed to install the Extension Pack /home/fred/Downloads/Oracle_VM_VirtualBox_Extension_Pack-6.1.16.vbox-extpack.
Result Code: NS_ERROR_FAILURE (0x80004005)