I just purchased the 2020 Premeier Elements Upgrade (I have a 2016 version on my macbook pro) and it will not install. It gets hung up at 3% and just sits there. I have a 2018 Machbook Pro running OS 10.14.6.
It is going to be hard to figure that out in a user forum because that is too odd to be common knowledge. Your best bet is to start a "chat" at https://helpx.adobe.com/support.html. There will be a little "start chat" icon in the lower right corner.