We have this same issue occur periodically when Quickbooks is forcing an update and does not even let us login to Desktop Premier 2020. I've read through these threads and find there is a communications gap in the conversations. Here are my comments:

• We do not get the "Install Now" and "Install Later" options-  just the "you don't have permissions" statement and a "Close Quickbooks" button. (pictures from QB Team on the support threads show the install buttons, but we don't get those). 
• QB team and thread contributors keep using the term "system administrator" or "Administrator", but they don't distinguish between the Windows desktop administrator and the QB software administrator. Those are 2 different things and 2 different sets of credentials.  That, I can see, is greatly confusing the issue. 
• With the error that you're receiving (and us as well), you will need a Windows desktop administrator ID and password (outside of quickbooks) to run quickbooks as a Windows administrator and do the update.  For us, this is a big beef we have with QB because our Windows desktop system administrator is not always available and not even part of our organization, so we can't access QB at all until we can track them down.  In order to upgrade, we have to right click on the Quickbooks app icon, select Run as Administrator, have the Windows systems administrator enter their Windows admin ID and password, then go through the appropriate upgrade steps. Once we verify the upgrade worked, we close quickbooks, then the Quickbooks administrator can login with their Quickbooks administrator credentials.
• Very frustrated that QB doesn't give the "install later" option and forces the upgrade now. Not everyone has quick access to a Windows system admin ID, especially if desktop support is outsourced.