If you don’t run a discord, one of your users will “helpfully” start one anyway and the community will go there. You’ve then lost control of your Q&A forum.
I have both an official Discord and Reddit. Discord was the only platform I didn't start myself, but eventually took over. My Reddit is as good as dead, Discord incredibly active.
The theory all sounds good, but the fact is that the community will pick the place they hang out, not you.