Kexts can't load, Parallels 17.0.4 oon MacOS 10.14.6

This likely started with the installation of 17.0.4 but I hadn't tried to start Parallels in a while, so it's hard to be certain.
When I tried to start it on Monday, I got the notice that I needed to go to Privacy & Security settings, unlock that with my password, and click Allow next to "Parallels International GMBH". But there is no Allow button there.
Parallels Support told me to click on the Advanced... button at the lower right corner, but (as I expected) that did nothing useful. There is still. no Allow button: