I don't know about 'seriously contesting' but Democrats are making a credible effort at least in that the party has rallied around Shawn Wilson, JBE's former Transportation Secretary.
Just because he hasn't held an elected office previously, I don't think he should be regarded as a writeoff.
https://www.wilsonforla.com/Louisiana governor’s race: Wilson campaign raises nearly $580K in 30 days
https://www.brproud.com/news/louisiana-governors-race-wilson-campaign-raises-nearly-580k-in-30-days/As the only Democrat of any profile running, he should at least make the runoff.
After that, it's unlikely he'll win, but there are paths to victory if he runs against Jeff Landry and especially against Stephen Waguespack who was Governor Bobby Jindal's Chief of Staff.