I am still using an older version Lightroom 6.14 on Windows 10 for the past few years. Last night I used the HDR function on some CR2 files and it worked fine. I went to use it again on some CR2 files this morning and it does not offer me the option of doing anything with HDR after clicking on the Photo Merge tab. Adobe help has been useless and suggested I post her. Any ideas? Thanks.
Adobe does not support Lightroom 6 at all. I have never used it. I went from Lightroom 5.7 and moved to Lightroom Classic. You could try resetting the preferences to see if that makes a difference. There are no updates or fixes from Adobe. 6.14 was the last update for Lightroom 6.