A forum, hell even a subreddit would be better, at least it wouldn't require an account to view and is indexable.
I think if you’re targeting developers, then Discord is fine.
If you’re targeting businesses, then you’d want a contact-us form at the bare minimum.
I'm a developer, and I find Discord to be a disorganized mess. I prefer a traditional support forum to Discord, and that's a pretty weak option.
And if you want to preach the virtues of FOSS of your product, you’d offer FOSS real-time communications as at least an option. Slap in IRC, an XMPP MUC, Matrix Space. You could bridge to (not from) Discord as a second-class option if it was deemed valuable, but shouldn’t be the primary host.
A phone is worse, but almost anything else is better: email, forms, old-school forums, discourse, github issues or discussions, etc...