As to “maybe 20”, it’s a great deal more than 20 in Sibelius’s various different contextual menus (which vary dependent on what kind of text you’re entering). In Dorico, if you’re entering metronome marks you should be using w/h/q/e/x etc. anyway; if you’re entering dynamics there’s (almost) no chance of not typing f/m/p/s as “music text”; swing triplets will eventually be handled by the tempo popover; accents and diacritics can and should be handled by the operating system. What does that leave? Oh, Zymbols, I guess, but those aren’t text - they’re more equivalent to Dorico’s Playing Techniques. In Dorico you can use any Bravura glyph as a Playing Technique. Once you’ve set it as default, which takes a matter of seconds, it’s in the right panel (or available via the popover) in any future project.
Dorico doesn’t have “text boxes”; it has staff and system linked text (Shift+X and Shift+Alt+X), and it has “text frames”. In text frames you can already right-click for accidentals.
I’m not entirely disagreeing with the sentiment, marco_polo, but your original post is pretty ambiguous. If you have a feature request, please at least describe which symbols you’re repeatedly having to copy and paste (or which symbols’ character codes you’re cutting and pasting into text frames, e.g. {@U+E266@} for triplet flats), and which kinds of text item you’re using SMuFL glyphs within.