On iCloud Drive (and Skype's web app), attempts to use Apple SF family fonts are not handled correctly, and fallback fonts are not used either. Instead, a default serif font is used (Times New Roman).

Steps to reproduce:

Sign into https://icloud.com and open iCloud Drive
Note that the most text is a serif font
On Safari & FF, the font is "SF NS Text"

Orion - iCloud Drive - note the font-family has a range of fallback fonts which are def available, but it goes with Times instead

Safari - iCloud Drive - fonts correct:

FF - iCloud Drive - fonts correct:

I made a simple webpage to test this and got weird results:

sf-fonts-test-pagehtml.zip

787B

There is a fallback font sans-serif specified and on Orion, Safari and FF, the fallback font is used (Helvetica), not the SF fonts. So at least the fallback is being handled correctly, though the behaviour is different from iCloud Drive.

I have tried compatibility mode, setting a different user agent (like FF and Chrome), blocking web fonts - nothing changes the issue

On other apple websites, the Apple fonts display correctly.

Maybe Apple lets their fonts be used on certain pages only? I cannot figure out what is causing the differences in behaviour

Expected behavior:
The font works

Orion, OS version; hardware type:
Orion 0.99.112.5-rc (WebKit 613.1.12)
macOS Version 12.2 (Build 21D49)
MacBookPro18,3

Session Info:

Open windows => 1
Pinned tabs => 2
Active window tabs => 20
Active tab url => https://orionfeedback.org/?q=font

Enabled Extensions:

Request Control (firefox)
MTG Quick Search (chrome)
Mate Translate – translator, dictionary (chrome)
SponsorBlock for YouTube - Skip Sponsorships (firefox)
Bitwarden - Free Password Manager (firefox)
Reddit Enhancement Suite (firefox)
Dark Reader (firefox)

Disabled Extensions:

Non Default Settings:

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ContentBlockerLastUpdated => 2022-02-02 00:00:00 +0000
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LastCrashCheckDate => 2022-03-09 03:31:00 +0000
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ActiveLibraryTab => extensions
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