/System/Library/Fonts/PingFang.ttc is the macOS default Chinese font. The file is a collection of three family names representing three regional glyph variants, PingFang SC, PingFang HK, and PingFang TC. FontManager doesn't seem to be able to find the SC family inside; I haven't tried the others yet.
(Manually constructing a fontProperties works, as demonstrated in #20251 (comment). However, it's not a solution for well-encapsulated code from other people.)
indfont: Font family 'PingFang SC' not found.
findfont: Font family 'PingFang SC' not found.
findfont: Font family 'PingFang SC' not found.
findfont: Font family 'PingFang SC' not found.
findfont: Font family 'PingFang SC' not found.
findfont: Font family 'PingFang SC' not found.
findfont: Font family 'PingFang SC' not found.
findfont: Font family 'PingFang SC' not found.
findfont: Font family 'PingFang SC' not found.
/private/tmp/1.py:5: UserWarning: Glyph 20320 (\N{CJK UNIFIED IDEOGRAPH-4F60}) missing from current font.
plt.savefig("test.png")
/private/tmp/1.py:5: UserWarning: Glyph 22909 (\N{CJK UNIFIED IDEOGRAPH-597D}) missing from current font.
plt.savefig("test.png")
/private/tmp/1.py:5: UserWarning: Glyph 19990 (\N{CJK UNIFIED IDEOGRAPH-4E16}) missing from current font.
plt.savefig("test.png")
/private/tmp/1.py:5: UserWarning: Glyph 30028 (\N{CJK UNIFIED IDEOGRAPH-754C}) missing from current font.
plt.savefig("test.png")
findfont: Font family 'PingFang SC' not found.
findfont: Font family 'PingFang SC' not found.
findfont: Font family 'PingFang SC' not found.
findfont: Font family 'PingFang SC' not found.
findfont: Font family 'PingFang SC' not found.
findfont: Font family 'PingFang SC' not found.
findfont: Font family 'PingFang SC' not found.
findfont: Font family 'PingFang SC' not found.
findfont: Font family 'PingFang SC' not found.
findfont: Font family 'PingFang SC' not found.
findfont: Font family 'PingFang SC' not found.
findfont: Font family 'PingFang SC' not found.
findfont: Font family 'PingFang SC' not found.
So the issue is probably this: addfont only adds one prop for a whole ttc. It should at least return one per unique family name. The FT2Font call upstream already ignores this possibility -- I think in FreeType2 API, the relevant thing is called a face_index.
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Artoria2e5 commented on Jan 26, 2024
Got the debug trace here:
out.txt
PingFang is only resolved to HK
So the issue is probably this: addfont only adds one prop for a whole ttc. It should at least return one per unique family name. The FT2Font call upstream already ignores this possibility -- I think in FreeType2 API, the relevant thing is called a face_index.
Indeed, PingFang HK works:

ksunden commented on Jan 26, 2024
Yes, currently we have only limited ttc support that only resolves the first font in a ttc.
See #23293 #3135
QuLogic commented on Jan 30, 2024
I'll close as a duplicate of #3135.
Artoria2e5 commented on Jan 31, 2024
Fair enough!