Googling even more shows many people find the same problem with no real solution. If I can't export what I see in Lightroom classic to various forums, or print within reason, onto photo paper then to me it is a waste.
You need to
- export in a format that supports HDR (such as JPEG XL)
- check the box in Lightroom to export using HDR, then
- view the image in an application that also supports viewing HDR files (such as the latest version of Preview on macOS Sequoia).
- view the image on a display capable of showing an HDR gamut.
All four need to be true before you will see the effect.
Web browser support is limited at the minute- of the mainstream browsers I think only Apple Safari supports display of JPEG XL files (N.B. I may well be behind the times about this, others may know better than me)
However, you may also find forum software doesn't yet recognise JXL files as a legitimate image file format, so you wouldn't be able to post the files.
When I try to upload a .jxl file to TP, for example, it's greyed out.
Similarly, Flickr doesn't recognise the file format if I try to upload there.
It's early days for HDR still. Support will probably come, but it takes time to overhaul a global technical ecosystem built around standard JPEGs and other SDR formats.
Finally, you are
never going to be able to print an HDR image onto paper and get it to display the full range of tones in the image. Paper cannot reflect back more light than falls upon it (which is what would need to happen). By definition, HDR operates beyond the range of paper printing (full black to full white).
Short of using some back-lit light boxes with cleverly masked apertures cut out of your prints, HDR is for on-screen display only.
