Yes, they are in scope but a "small community forum" has nothing to do but to fill and keep a few self-assessments just in case. There is no requirement to implement age verification across the board (hence why current official guidelines target only porn sites in relation to age verification).
You are being facetious as "priority illegal contents" are the sort that are the ones that are obviously very unlikely to be encountered on a "normal" small community forum. So this is no more than a box-ticking exercise, really.
Regarding age verification, the OSA is explicit states that if you ban all such content in your T&Cs you do NOT need to have age verification.
