First, SE is not designed as a traditional social media platform. Thus, traditional 'user engagement' doesn't exist here. That's simply not the purpose of it. It's a more question/answer platform and less away to shout out inane unfounded opinions.
That said, it wouldn't hurt to have a little more activity here. Perhaps you might look at other hobby-specific SE sites that are more "successful" . For instance Photography SE does a weekly "Photo Of The Week" that is a great way to engage any user in a positive way that isn't completely restricted to question/answer. Perhaps try a similar routine i.e. 'recipe of the week' or 'brew rig picture of the week', etc etc.
Today- 'user engagement' is dependent on the user. If the user has no immediate brewing question..there's nothing here to engage with.
Lastly- figure out what kind of user engagement you want. I was once a big contributor to other online homebrew forums (reddit specifically) and left because they're terrible. The content is lacking any depth, the community is toxic, and actual brewing information is less popular than whatever meme-ey clickbait brewing crap floats to the top. /rant