I've tried MusicXML as a way of porting to Notion but I found that the result was very inaccurate. In particular Notion does not seem to handle staves with more than one voice, and stacks the second voice at the end of the bar, thus making the bars double the size and the score unusable.
There may be settings somewhere I didn't see or didn't get right, but otherwise I can only hope that XML import will improve.
I also tried loading MIDI files created in Sibelius, and to my surprise found that was inaccurate as well. Of course with MIDI you also end up with all sorts of strange rhythmic and pitch mis-spellings, which take an age to correct.
So I've ended up having a copy of Sibelius on screen, a copy of Notion running, and a strip of magnifier across the top (because I'm visually impaired and Notion's zoom doesn't get big enough for me). I re-input the notes - laborious, but the only way of (a) getting some of my scores to sound well and (b) the only way I can compare the products.