The challenge here - for both Dorico and for any engraver - is that there is no standard symbol(s) in use. One of my teachers used an inverted diamond - pointing down - for apoyando, and a u-shape for free tirando. Neither seem to have caught on beyond his students. I’m not saying it’s not a good idea to notate these, but one would have to give information in the form of a preface/footnote what the symbols indicate. In fact, I read the first measure of the OP as simply tenutos - yes, they should be above the notehead, and not the right hand fingering - but that was my first thought. For the second measure, I took the symbol to be some type of accent.
The other point I would make is that these indications are really only found in pedagogical works - one rarely sees concert pieces with any indication of which strokes to use in any situation. In pedagogical works, there is nearly always text that accompanies the examples. But in music for performance, it is not seen (much).
Again, not that it’s a bad idea, but there is the risk of a lot of information that could be applied to a single pitch: fret, string, left hand finger, right hand finger, and now rest/free stroke. We may be generating more problems than solving them.
FWIW, I am a guitarist.