SplitButton: menu pass-through not working again

[jh-aimpera]

Describe the bug

For the SplitButton the pass through to the menu is not working as expected.

<SplitButton
  label='Save'
  model={[]}
  pt={{
    menu: { className: 'where-am-i' } // This class is not applied to the menu.
  }} />

Seems like after the fix from #7259 this bug is appearing again.

Reproducer

https://stackblitz.com/edit/vitejs-vite-stg96iza?file=src%2FApp.tsx

System Information

System:
    OS: Windows 11 10.0.26200
    CPU: (22) x64 Intel(R) Core(TM) Ultra 9 185H
    Memory: 25.42 GB / 63.61 GB
  Binaries:
    Node: 24.11.1 - C:\nvm4w\nodejs\node.EXE
    npm: 11.6.2 - C:\nvm4w\nodejs\npm.CMD
    pnpm: 9.12.1 - C:\Users\jonas\AppData\Roaming\npm\pnpm.CMD
  Browsers:
    Chrome: 142.0.7444.176
    Edge: Chromium (140.0.3485.54)
    Firefox: 144.0.2 - C:\Program Files\Mozilla Firefox\firefox.exe
    Internet Explorer: 11.0.26100.1882
  npmPackages:
    primereact: 10.9.7 => 10.9.7 
    react: ^19.2.0 => 19.2.0 
    tailwindcss: ^4.1.17 => 4.1.17

Steps to reproduce the behavior

No response

Expected behavior

No response

[Coderxrohan]

@jh-aimpera

I verified this on the current master branch.

The passthrough is correctly forwarded from SplitButton to the internal
TieredMenu via pt.menu. To apply a class to the menu container, section-based
passthrough must be used, e.g.:

<SplitButton
  pt={{
    menu: {
      root: {
        className: 'where-am-i'
      }
    }
  }}
/>

Using pt.menu.className does not target a valid TieredMenu section, which is why
the class is not applied. With pt.menu.root, the class is correctly added to
the menu root element.