Add "User" text styles to Inspector dropdown for fingering

" Is there a real world use case where the available styles are not sufficient (given that, of course, you can customize them)?"
Sorry, I do not really understand this. I have not really follow during the development of 3.0 all these changes about text styles. And so, I cannot follow your explanations satisfactorily.
I was simply here the relay of a testimony. I understand that the user complains that, in the 3.0, he cannot do somethings to customize fingerings with the Inspector drop down, while he could do it with 2.3.2. Do you agree with that (it would be an introduced limitation?), or have I missed something?

User's reply (I asked him what style he used in the 2.3.2, and for what reason.) What I see on the picture below is that he created a custom style (two en fact, LH and string number)
I quote the reply: "Sure, the offset left hand fingering that I mentioned above is probably the one I used the most. When I wanted fingering just above the note (and not to the left, or above the beam) I used this: "

So, after a few tries.
Example, I go to Format / Style / Text styles, I create a new style with certain settings let's say for particular lyrics, eg "User-1-lyrics".
Then, in the score, I select all lyrics. In Inspector, the drop down gives me access to all text styles, including my new "User-1-lyrics"
But, if I do the same thing with a new style for Fingering and some settings (size, X/Y) let's say "User-2-Fingering." And then I select all similar fingerings: result, in Inspector, the drop down does not display other styles, other than fingerings, AND also my new "User-2-Fingering" style is missing.
Did I understand the problem (and the one the user encounters too), or did I miss something again?

1) "So the user desn't just want to change the LH fingering style, he wants a choice between regular LH fingering and his custom version, correct?"
That's right.
User's new reply, I quote: "Yes, I wanted to keep the default fingering styles and leave them "intact", simply adding my new style preference to the list of choices. I think I understood at the time that I could have done it the way you suggest [note: I suggested to create a template with custom fingering] but chose not to. In 3.0, that option seems to have been removed, so I'm trying to understand what the program would rather have me do."

2) "I already submitted a PR to change the default back to being next to the notehead. It shouldn't be hard to make it also move the fingering up a space if there are multiple voices. And, presumably, down for voice 2, as shown in the picture? Looks nice to me, but I don't know if that's the most common arrangement or not."

The expected default (most common display) is to the left, as for the versions 2.x - see images below.

Other point:
And for my part, I would vote for number strings be moved by default below the staff (and not above as currently). They are rarely used to indicate string 1 (and thus presumably for a note or notes entered in Voice1), but to indicate an alternative solution to the location of a note.
For example, D 5th fret 5th string, instead of a D 4th open string (as shown second image, end first measure). And so all these notes are most often in voice 2/3/4, and therefore the indication of the string number is naturally below or within the staff (you can see other examples on the same attachment), but not above.

Ok, hoping it does not take too long. Because right now, it's just a pain to move at the good place the LH fingerings one by one. In a few words, to pass them over the stem (when it is up) and get them to the left down near the notehead. It takes two-three seconds each fingering. In short, it's discouraging, and I gave up, waiting for better days.