First post here and I can imagine this question's been asked a thousand times. I get the same message every time I open PSE 11 but there's no way I can find to actually speak to someone at Adobe. So is there anything to be done to update/upgrade to 64 bit from 32 bit?
Have you upgraded Mac OS to Catalina? Is PSE11 still working?
Sometimes pre-existing software will continue to work after upgrading MacOS, despite Apple warnings. PSE11 is a 64 bit app but the installers and licencing app are 32 bit. So just ensure you never sign-out from the help menu. Never un-install the software as re-installation will be impossible on Catalina.
There will be no updates from Adobe for older software. You could consider an upgrade to the recently released PSE2020 which is the only version which is now supported.
You can try free for 30 days before purchasing an upgrade. What’s New in Elements 2020
This is nothing new and Apple has been pushing out warnings for months that updating to Catalina will affect 32 bit apps. PSE11 is quite old and was never designed for Catalina so this comes down to user choice. Like you I’m sticking with Mojave for the time being. Even though I have Elements 2020 I’m not sure my Nik Collection plug-ins will continue to work.