Indeed "flop" traditionally denotes a "total or spectacular failure". For a movie, the term is usually applied to one that absolutely hemorrhages money and/or one that is infamous in its production or marketing missteps (which sometimes includes movies that eventually show modest profits like Waterworld). This movie was (probably) only a modest failure, and its modest failure caught no real mainstream attention. It's a bummer for those of us wanting sequels, but it probably won't kill any careers, nor make Hollywood studios substantially more anti-pseudo-medieval fantasy than they already were. It is simple, garden-variety financial failure. And really, long term, as a movie well-received by most people who did watch it and tied to a popular IP, it is likely to have substantial ongoing value, even if Paramount and Hasbro continue failing to really make the most out of it in the near term. .
And the reason the terminology matters, is because "flop" is also generally associated with a movie that was utterly doomed to failure, not a movie that has solid fundamentals but just didn't find its audience due to marketing, timing, or subtle shifts in audiences' cinema preferences.
In my opinion the movie had strong enough fundamentals. It's not the D&D movie I would have made, but everything about it seems carefully attuned to be an audience pleaser in 2023, and we should all accept the fact that if this failed our own personal pet versions of what it should have been would have almost certainly failed harder. So that leaves it being a failure of circumstance rather than fundamentals. I think it probably should have either released a few weeks earlier (to take advantage of spring break moviegoers) or else been a Summer or Holiday release. I think while the marketing seemed good, it gave a lot of people the impression that this was spiritually a knock-off Marvel movie more than it really was, and audiences seem to have fatigue for actual Marvel movies. But I think the biggest issue was simply the insurmountable one that 2023 has a post-COVID movie glut at a point where movie-going is in decline, and its just very slim pickings out there for anything that doesn't manage to be one of the big event movies (which for me it was, but clearly not for most people).
In summary, it was a modest failure, not a huge one, and not one that teaches us a clear lesson about why it failed, nor a failure that marks it as clearly incapable of being a hit. If it was a flop that might be instructive, but it was just a moderately unprofitable movie, as many movies are.
