Personally, I wouldn't let large breed pups do stairs regularly until after they are hip scored at 1 year of age. And even then, I'd want to walk with them on the stairs to ensure they take them slowly.
This study found that dogs using stairs regularly had a higher incidence of hip dysplasia:
https://pubmed.ncbi.nlm.nih.gov/22620698/ "Puppies walking on stairs from birth to 3 months of age had an increased risk of developing HD. "
We don't really know how long after this, the stairs are a factor - since the study stopped at 12 weeks. So it's not safe to conclude it's ok after that....