Premiere elements 2020 update not working

If you can't install the update, it is not typically significant.  The primary updates the last few years has be for the Adobe Camera Raw tables as new cameras came out.  So unless you are making slide shows with RAW still files, you are not missing much, if anything.

In the past the advice has been to Download the 'trial' and enter your serial number to activate, since the trial will include the latest update
https://helpx.adobe.com/download-install/kb/photoshop-elements-downloads.html
https://helpx.adobe.com/download-install/kb/premiere-elements-downloads.html

HOWEVER... now that version 2022 is out I'm not sure if 2020 is still available

If not, try here

https://community.adobe.com/t5/download-install-discussions/older-versions-pre-2020/td-p/13065324

IF/When you do have a download, be sure to copy it to AT LEAST one external device
-you should ALWAYS keep a copy (or two!) on an external device
-since Adobe DOES SOMETIMES REMOVE OLD VERSIONS FROM THE SERVER
-a usb flash drive or external hard drive, or write to a CD or DVD
-plus a text file containing your serial number if you have a serial number program