@SciresM has added support for Switch firmware 6.2.0 key generation to hactool v1.2.2
The quote below is from his Twitter:
The new tsec_root_key was retrieved through an unpublished exploit and these changes were made to add support for the new firmware. Since the keys are still kept private there is currently no custom firmware out which supports 6.2.0, so keep that in mind while avoiding the update from Nintendo.
NEWS SOURCE: Switch FW 6.2.0 keys out in the wild (via) EurAsia
(Our thanks goes to hitman43 for the heads up.)