Before You File a Bug Report Please Confirm You Have Done The Following...

• I have tried restarting my IDE and the issue persists.
• I have updated to the latest version of the packages.
• I have searched for related issues and found none that matched my issue.
• I have read the FAQ and my problem is not listed.

Playground Link

https://typescript-eslint.io/play/#ts=4.9.3&sourceType=module&code=KYOwrgtgBAogHgQwgBwDbBuCBZAlnYAEygG8AoKKAFQAtcBnKAXigEYAaC6mhAF2agByAEyDOAXzJkAxgHsQ9fgHdcvGpkgCAFADcEqMMAD8ALliIU6DTnxEAlMwB8pLrgBmUXfsMOSUSeJAA&eslintrc=N4KABGBEBOCuA2BTAzpAXGUEKQAIBcBPABxQGNoBLY-AWhXkoDt8B6ZfKsugIwHs+SAIZN6AD2LQUySnyaoMAbUgB3IdCaQANJihD48PioByCeEJ5IAok1gBbdGE6xEYAL4BdcO5BugA&tsconfig=N4KABGBEDGD2C2AHAlgGwKYCcDyiAuysAdgM6QBcYoEEkJemy0eAcgK6qoDCAFutAGsylBm3TgwAXxCSgA

Repro Code

enum ExampleEnumMixed {
  This = 1,
  That = '2',
}

const withEnum = (value?: ExampleEnumMixed) => {
  if (value) { }
}

ESLint Config

module.exports = {
  parser: "@typescript-eslint/parser",
  rules": {
    "@typescript-eslint/strict-boolean-expressions": ["warn", { "allowNullableEnum": true }]
  }
};

tsconfig

No response

Expected Result

No warning for the if statement

Actual Result

Warning from strict-boolean-expressions rule with { allowNullableEnum: true } option appears.

Additional Info

Similarly to what has been done in #6618, we should also consider mixed enums in allowNullableEnum option.