The Steam forums are limited, but they could be useful as a temporary stop, throwing a bridge towards a more permanent solution. Plus almost everybody has a Steam account.
Personally, I’d perceive a subreddit as something more stable and alternative to a forum.
It could be an interesting experiment, though one that has the potential to split the core of the community, so that’s a step to think long about IMO.
I can’t think of any other free alternatives, that are popular and close enough to a real forum, outside of whatever is left of those sites which sold forums based on a freemium model.
As much of the technological landscape is driven by people who feel a strong drive to become billionaires before they hit their 30s, it tends to be littered with SaaS models that follow the conventional convenience-uber-alles paradigm, IOW traps waiting to trigger, in all likelihood.
The main difference is that joining an existing community means subscribing to their cultural contract, adopting their ways and habits, and so on. This may be coming on a little strong, but in a way, you get assimilated.
I’m sure those of you who’ve been part of several forum or forum-like communities, must be familiar with how the average person tends to behave differently depending on the context, often subconsciously.
That is to say, there is no guarantee that after transplanting the seed of a community into an existing one, its characteristic traits will remain recognizable (I’m not saying identical, as everything is in flux, ofc).
Plus, whoever runs that community gets to make all the decisions, from whether they want to invest in it or not, when they’re sick of it (or of you in particular), want to shift to a different, new platform that is not quite like a forum, down to whether to shut down tomorrow so kthxbye.
Moving an existing community to a new place of its own can be riskier in some ways, but may off-set some of these potential effects I’ve mentioned.
Realistically, it’s pros and cons that need to be evaluated carefully in order to make the best decision.