There are only nine bars in the project you attached, and no harmonics in there. But it’s expected that some harmonics would produce fractional fret positions.
I was able to solve some (but not all) of your problems
First, at rehearsal A: To fix the question mark, select the D, open up properties, and look under “Notes and Rests” for the String property. Switch it on, and make sure 4(D3) is selected. For me, it took care of the problem. Dorico couldn’t figure out which string to use for this note, probably because it is possible to play the exact same harmonic on the 6th string.
Second, rehearsal B: To get this harmonic to the right fret (19), select the note and again take a look at properties. There is a category for Harmonics, and the one you’ll want to look at is “Node.” Switch it on, and use the arrows to switch to 2. Basically, Dorico always chooses the harmonic node that is lowest on the fretboard, so if there is more than one way to play the same harmonic, you’ll have to change the node to a different number to get the one you want!
…which brings us to your 3.9 harmonics. For whatever reason, Dorico doesn’t seem to see 4th and 9th fret harmonics the same way guitarists do. I did try changing the node in properties (as I did above), but Dorico comes up with fret 8.8. While this may be mathematically accurate, I do think that there probably should be a way to either override this or ask Dorico to “round upwards.” I don’t have an answer for you here, I’m afraid!
Hope this helps!
Beautiful music, by the way!
Take a look at m. 4: I’m guessing that those second fret notes are supposed to be on different strings? If so, you can use M to move them to the lower strings (N moves tab numbers up).
Sorry for offering an unsolicited opinion, but I have inputted enough guitar music to spot this kind of stuff pretty quickly.