Even though the traditional forum format is old technology there is still no better platform for long form content. I have been tracking a number of ASX based Facebook Groups for a number of years now and most of the ones that were busy in 2018 have either been abandoned or now have minimal activity.
I belong to one or two other Facebook Groups that are not investment related and the one that is most useful to me is a local community group where people ask for recommendations for various kinds of local transpeople, or to find a lost pet. Facebook Groups is perfect for that. Short questions or queries that require short answers. But it is not suitable for long form content, extended discussions or content that involves multiple images or other media to be inserted into it. There are threads here that have been running for 18 years and have thousands of replies. This kind of content is not suitable for Facebook Groups and is where traditional forums shine.
Regarding forum software generally, I have been using it as a user since 2001 and as an administrator since 2004. For the longest time there was very little advancement in the core features and functionality available in most commercial forum software packages, but that has been changing in the last five or so years most probably in response to the proliferation of other competing platforms. It is becoming more advanced, and more extendable through free and paid add-on modules that provide additional features and functionality and I expect this increased pace of development to continue for the forseeable future. Forum software will continue to get better.
A few years back I was quite pessimistic about the future of forums, but now I am not so sure. The interface may change over time, but online community software built for long form content and extended discussions isn't going anywhere because there are many niche areas that require software that caters to this kind of content. Also, people are becoming more wary of social media generally and there are a lot of people who don't want to post under their real name on large social media platforms. Forums are built for privacy. Nobody here knows who anyone else is, unless they voluntarily choose to reveal their own identity. The anonymous aspect of forums is very appealing to a lot of people and I imagine will continue to be in the future.