HDR

Do not use HDR editing if your aim is to print the resulting image. Printers cannot print the highlights gain that HDR gives. They would need to use paper that emits light...

It’s not expected that you can just click HDR and it’s done. Because HDR extends the highlight range by up to 4 stops and can cause many adjustments to be recalculated for that extended range, usually you want to recheck the image to make sure it still looks the way you want after clicking HDR.

When exporting, you now want to think about where it's going, because HDR support is not yet everywhere.

If you know it's going to be viewed only using HDR displays/apps, then you want to make sure you picked one of the export file formats that can reproduce the HDR highlight range.

If you know it’s going to be viewed only using SDR displays/apps, then you need to go back and click “SDR Rendition Settings’, enable “Preview for SDR Display”, and tweak the SDR rendition settings so that you can make it look better on non-HDR displays, and then pick one of the SDR export file formats.

If you want to make it look good in both HDR and SDR displays/apps, then you can do the previous paragraph, but also choose an export file format that can reproduce HDR and also include a gain map for SDR displays.

If this is all too confusing, read the Adobe tech article about how HDR works, which explains a lot of the above in more detail:

High Dynamic Range Explained

Greg Benz explains more about gain maps and other details:

Create and edit true HDR (High Dynamic Range) images