Apple has been popping up a dialog box saying almost exactly that every time you launched a 32-bit app, including Safari extensions, for a year now. I've seen a warning about my 32-bit extensions multiple times in the last year. This is not news. I just got bit because I didn't realize that Safari 13 was the cut-off—I thought I was fine until Catalina (and am planning on holding off on installing Catalina until I'd created a virtual machine for my old software, for exactly that reason).
Similarly, Evernote has known for at least a year that macOS 10.15 would break 32-bit software, and there have been hints that this was coming for more like 3 years. Since 64-bit Evernote would've worked just fine any time in the last decade, there's really no excuse to be waiting until the last possible week to release an updated extension. They could've made this switch 6 months ago and been just fine now.
One question I still have: will I need to switch over to the Mac App Store version of desktop Evernote in order to get the new Safari web clipper? Or will the version we download from the web still work (once it's updated)?
And in terms of feedback: add me to the list of people for whom the web clipper is the #1 reason I use Evernote, and the excellent functionality of that web clipper is why I'm using Evernote rather than a competitor. If that goes away, or works less well, I may switch software.