I will admit that my computer is behind the times. An old HP Pavilion, 8 GB RAM, no separate graphics card, grossly underpowered by today's standard. When the enhance details feature was introduced my computer handled it without a problem. However, after the 8.21 update, the dialog box displays but there's just a spinning whatever that keeps on spinning. I know, I need to upgrade my computer, but this was a noticeable change after this last update. I'm using Windows 10, incidentally.
On further investigation, I find If I click on the enhance button even though the preview never displays, the enhanced DNG is created as before. Not a big issue I suppose because the display really didn't show anything of significance. But I believe the file has some benefit when preparing for printing. At least that is where I have seemed to find benefit with the enhanced DNG file so far.
Thanks James. Good to know it is working for you now. Although ideally it is a good idea to run EnhanceDetails on an unedited raw file as that will give you a better idea of whether it makes a difference on that image or not, it should still work on edited images. So we will work on fixing this issue.
Perhaps restarting LR or your system freed up some memory? I've noticed strange behavior sometimes in LR and simply closing and reopening it returns things back to normal. I Have 32 GB of memory so not likely that was the cause for me or perhaps you as well with only 8 GB.
I thought about that. I had restarted Lightroom, shut down the computer and restarted it, and done everything that I could think of, and I "thought" I had covered all the bases. Apparently I hadn't. Wish I could simply add more RAM, but that's all the motherboard will accommodate. Maybe an upgrade for the computer later this year. We'll have to see.