What matters more is the rate at which content is generated, and I think GH has a pretty competitive story considering that people naturally want to ask the project maintainers/community questions directly (as evidenced by all of the GitHub Issues which are formulated as questions) and considering GitHub's significant share of those maintainers/communities. I posit that new content will increasingly appear on GH Discussions.
Please don't mistake this for some exaggerated "GH is going to kill SO" argument--SO will do fine, but there is a compelling story for why MS wouldn't spend $1bn on SO.