Hello grub@gnu and thanks for your little bit of magic. I have a problem.
I hope the screenshots attached will answer many of your questions, but as background:
+ Linus Mint 20.3 (Cinnamon) on a Lenovo T480, installed on the onboard SSD running LUKS.
I suspect it's the LUKS that's at issue, I've used :update-grub lots of times without any problems on simpler configs.
You may already have a solution, or possibly someone else has reported this. I honestly doubt that I'm the first. If you have news I'll be very happy to hear it.
Again, thanks for your project and its results.
Tim Rutherford