Interesting mix up there on the ‘event’ nomenclature 
So HubSpot’s native Facebook pixel integration just handles the pixel itself and will track page views and generic browser events, but it doesn’t take your HubSpot form submissions and push them to Facebook as conversions.
Since you’re trying to avoid GTM, you might want to look at tools Converly (disclosure: I’m the founder). It’s basically like HubSpot’s Workflows builder, but for conversion tracking. You pick a trigger, like a HubSpot form submission, and pick an action, like sending that conversion to Meta.
There are a couple of reasons why it might work for you where other solutions haven’t:
First, it sends the conversion server-side, straight to Meta’s Conversions API. That means ad blockers and browser privacy restrictions (like the ones in Safari and iOS) can’t get in the way and cost you conversions the way they do with a browser pixel.
Second, it captures everything Meta needs for a high Event Match Quality score. That includes the Facebook click ID (fbc), the Meta browser cookie ID (fbp), plus the user’s IP address and user agent, along with hashed contact details like email and phone. Meta uses all of that to match the conversion back to a person, and the more of it you send, the better the match quality and the more useful the data is for optimisation.
Third, it gives you a full conversion log. You can see exactly what data was captured, what got sent to Meta, and whether Meta accepted it or returned an error. You can also set up email notifications so if a conversion ever fails to reach Meta, you’re the first to know rather than finding out weeks later when the numbers look off.
Net result is much more reliable conversion data flowing into Meta than any pixel-only setup will give you, which means Meta has more (and better quality) data to optimise against, so it can deliver your campaigns more efficiently and bring in more leads at a lower cost.
Quick disclosure: I used AI to help draft this reply because it writes better than I can, but I reviewed and edited it myself before posting.