Please add "pf" dynamic - per SMuFL glyph (U+E52E - dynamicPF)

In 3.3 RC, the symbol is already listed in the master palette under symols/dynamics, it just isn't defined by MuseScore. It is quite rare, so I don't blame the programmers for not putting it in there much like a large number of other rare symbols. If you want it in your palette, currently you can define it's velocity and velocity changes and put it in a custom palette for future use. If 3.3, you will be able to put it in any palette.

Not just 3.3RC, in all MuseScore 3 version in the Master Palette > Symbole > Dynamics. And in MuseScore 2 too (but there's no Dynamics subsection, search for "pf")

pf is actually the only dynamics glyph missing from the 'regular' palettes

Search Wikipedia page Dynamics (music) for pf. You will find:

The fortepiano notation fp indicates a forte followed immediately by piano. By contrast, pf is an abbreviation for poco forte, literally "a little loud" but (according to Brahms) meaning with the character of forte, but the sound of piano, though rarely used because of possible confusion with pianoforte).

no!
The Wikipedia article confuses two things:
If "poco forte" or "piu forte" is abbreviated, it should be abbreviated as p.f. Because there is a space character between the two words. (in fact usually poco and piu aren't shortened).
examples:
"poco piu largo",
"poco piu piano" <= not ppp or p.p.p
"poco rit."
"poco a poco crescendo"

The word "pianoforte" used as a dynamic sign doesn't have a space character. in this case there isn't need to insert a period character between the two letters ("pf").

Additional note: If the instrument Pianoforte is written as an abbreviation, it must be abbreviated as Pf or PF. <= The first letter is uppercase.

The real reason for it is rare: it is useless.
The "fp" dynamics is very easily heard and recognized (such as accents).
However, you can't easily notice the "pf" dynamics (as there is no reverse accent). Most of the time you may even think of a mistake of the player.

Not everyone agrees with your statements.

I. In 1789, Daniel Gottlob Türk explained in his piano school (first chapter, fifth section, §79) the pf as
"1) poco forte, a little bit strong, also probably 2) più forte, stronger"
but not piano forte, weak strong - as explained in some instructions.
See
- IMSLP Klavierschule (Türk, Daniel Gottlob),
- file attachment and
- blog of G. Henle Verlag: "Smfz" - For some unusual dynamic statements in our Urtext editions in
https://www.henle.de/blog/de/2015/09/28/dynamikanweisungen/

II. In his music lexicon of 1882 Hugo Riemann points out that the abbreviation pf found in scores does not stand for piano forte or pianoforte, but for poco forte.
See https://musikwissenschaften.de/lexikon/p/piano-forte/

III. In Meyers Großes Konversations-Lexikon, Volume 6 Leipzig 1906, p. 793 under Forte:
poco f. (pf), "somewhat strong", formerly used as a level between p and mf (pf is not to be understood as "piano f.").
See: http://www.zeno.org/Meyers-1905/A/Forte

IV. In http://www.pian-e-forte.de/texte/vrtrgbzchng.htm you can find at DYNAMIK:
pf - poco forte (pocko forte), a bit loud (rarely used)

Do you see any p.f. in the given references?

See https://github.com/musescore/MuseScore/pull/5436
Implements pf basically as the opposite of fp, i.e. starts as p iano and continues as f orte

Das ist es, was ich mit meinen (mühselig ins Englische übersetzten) Kommentaren verhindern wollte.
Nun, Sie bleiben also ein Anhänger der gegnerischen Lehre, und wer bin ich, mich auf Glaubenskämpfe einzulassen.

The orginial request claims:
In some music scores the dynamic "pf" occurs, meaning "an instruction to play piano and then, suddenly, forte".
So that is what is needed and what my PR provides, but once that pf is in (that PR got accepted and merged), you're free to change its velocity settings to your heart's content (on an individual basis or in a custom palette).

You claim:
poco f. (pf), "somewhat strong", formerly used as a level between p and mf (pf is not to be understood as "piano f.").
Maybe, but that's what nowadays mp is used for and that is available.

As simple as it is to change effect of pf I think Jojo has done the best thing since most people would look at the pf and play it as the opposite of fp without any further explanation.

I just came across another example from: "Volksliederbuch für gemischten Chor", Leipzig: C.F. Peters 1915.

See attachment or IMSLP: Still, ihr Winde, still geschwinde (Wüllner, Franz)

Do you think someone can sing the third-to-last bar "piano and then, suddenly, forte" while thinking of the text "silent"?

Fixed in branch master, commit 3e5d9da940

_fix #296203: add "pf" dynamic

basically as the opposite of the "fp" dynamic_

Fixed in branch master, commit c746cd19a5

_Merge pull request #5436 from Jojo-Schmitz/dynamic-pf

fix #296203: add "pf" dynamic_

Automatically closed -- issue fixed for 2 weeks with no activity.