First report about ARC showing only 12 results for a genre was in September 2022 (and there were a number of posts about it later), and it’s still the case:
This was a year ago:
And the only way in ARC to list a genre (12 items of it) is through an album‘s or artist’s Info tab and the genres there, AFAICT, and there’s a feature request also from September 2022:
[Edit: not true, just awkward to find, see @dhusky‘s post below]