The forums are a good place if you focus on threads where you post panels, pages or talk about your comic, or ones where there's a theme like "post magical girl series!" or "post action series!" etc. Tapas Discord isn't great because the promo channel moves way too fast. Participating in events is more useful there.
Twitter used to be good but... yeah, it's a trashfire right now and it's way harder to build a following than it used to be. Instagram is a lot worse than it was, but worth a shot, and some people find Facebook okay. The big one right now is actually Tiktok; you'd be surprised how many subs even simple tiktoks filming your screen or participating in memes can get you.
If you don't mind spending a couple of dollars a month and making some banners, Comicad can be worth a shot too. I've found it pretty effective.