Not a licensing problem, I don't trust Apple to keep Catalyst working and I don't want to be in the position of spending a lot of time/money supporting a free Mac version if and when they break it. (this has been an issue for a bunch of people who cheerfully enabled their iPad apps on visionOS e.g.) Also, I am absolutely, fanatically opposed to the idea of centralized app stores, and would never consider distributing Pleco through one on a platform like macOS where it's viable for us to distribute our app directly.
As far as the immediate problem, I've been pretty consistent that we planned to do a Mac beta once we had this big easier-to-use revamp of 4.0 done, the main hold-up is that that's taking a long time. (partly for technical reasons, partly personal ones) But I'm glad that iPhone mirroring is proving a satisfying solution in the meantime, and it has the notable advantage over a dedicated Mac app of not requiring any sort of data sync; I could well imagine that even post-Mac-app, at least until we have a sync service a lot of people will prefer that over an actual desktop app.
As far as the immediate problem, I've been pretty consistent that we planned to do a Mac beta once we had this big easier-to-use revamp of 4.0 done, the main hold-up is that that's taking a long time. (partly for technical reasons, partly personal ones) But I'm glad that iPhone mirroring is proving a satisfying solution in the meantime, and it has the notable advantage over a dedicated Mac app of not requiring any sort of data sync; I could well imagine that even post-Mac-app, at least until we have a sync service a lot of people will prefer that over an actual desktop app.