If your Mavic is filming at 23.98, you should setup your LumaFusion project to the same frame rate in the master settings panel.
In case you don’t know (and hey, it’s the internet, so who knows what you know), the 24.00 frame rate was really created to be the standard for film projection when sound was added at the end of the silent film era. It’s really only intended to be used for that particular projection purpose, and not as a “video” frame rate. 24 frames is the film standard because, essentially, it’s the slowest frame rate that, when projected with sound, gives the “illusion” of smooth motion and good sound playback. Any slower than that, and the viewer begins to sense the “stutter” of the individual film frames, and the fidility of the sound track is compromised, destroying the effect.
And as an interesting side note, the film frame rate is not faster than 24 frames per second because hey, film studios back in the day wanted to spend as little money as possible. If they could get away with 24 frames instead of 30, that saved them six frames for every second of film. Multiplied over countless prints for editing, screening, etc., that’s a lot of money.
Sorry. I film-geeked out there for a moment. It’s been a long day of filming and editing, so I also may be “mis-remembering” what I learned in film school.