Can't use global theme overrides for Button disabled

Duplicates

• I have searched the existing issues

Latest version

• I have tested the latest version

Current behavior 😯

When using global style overrides to target the "disabled" css slot on a Button like so:

const theme = createTheme({
  components: {
    MuiButton: {
      styleOverrides: {
        disabled: {
          fontSize: "55rem"
        }
      }
    }
  }
});

The global style override does not apply.

Expected behavior 🤔

Any styles contained in MuiButton.styleOverrides.disabled should be applied to a .MuiButton-root.Mui-disabled.

Steps to reproduce 🕹

Steps:

1. Open https://codesandbox.io/s/globalthemeoverride-material-demo-forked-dpvi1?file=/demo.tsx
2. Observe output: the font size should be gigantic (55 rem), but is clearly the default font size, meaning the override failed

Context 🔦

No response

Your environment 🌎

 System:
    OS: Linux 5.10 Ubuntu 20.04.3 LTS (Focal Fossa)
    CPU: (12) x64 AMD Ryzen 5 5600X 6-Core Processor
    Memory: 8.35 GB / 12.43 GB
    Container: Yes
    Shell: 5.0.17 - /bin/bash
  Binaries:
    Node: 16.13.0 - ~/.nvm/versions/node/v16.13.0/bin/node
    Yarn: 1.22.15 - ~/.yarn/bin/yarn
    npm: 8.1.0 - ~/.nvm/versions/node/v16.13.0/bin/npm
  Managers:
    Apt: 2.0.6 - /usr/bin/apt
  Utilities:
    Git: 2.25.1 - /usr/bin/git
  IDEs:
    Nano: 4.8 - /usr/bin/nano
    VSCode: 1.62.2 - /home/ian/.vscode-server/bin/3a6960b964327f0e3882ce18fcebd07ed191b316/bin/code
    Vim: 8.1 - /usr/bin/vim
  Languages:
    Bash: 5.0.17 - /usr/bin/bash
    Perl: 5.30.0 - /usr/bin/perl
    Python3: 3.8.10 - /usr/bin/python3

Start by reproducing the issue in the linked CodeSandbox and inspect the MuiButton handling for global style overrides and its disabled CSS slot. Confirm the expected .MuiButton-root.Mui-disabled selector behavior, then add a regression test if the existing Button test structure provides one. Done means the 55rem override is applied to the disabled Button.