We are sorry about the experience due to Lightroom Classic crashing while peforming an HDR merge.
Since when are you experiencing this issue? How many images are you using to perform the HDR merge? Have you tried reducing the number of images to check if that helps? Are the images stored on your computers local storage or an external drive?
It would be helpful if you would share a screenshot of the error. You can also try creating a new catalog and import a few images to it and perform an HDR merge on them to check if you experience the same issue.