How to check users in Azure Active Directory group with Modern Forms and List Actions

We have added a new placeholder [[@User.IsMemberOfAADGroup('Type existing Azure AD group name')]]

Note 1: to properly use this function users have to allow third-party cookies in their browser
Note 2: Nested security groups are not detected by this function

To use this function placeholder, you have to approve the Directory.Read.All Graph API request from Solution Studio in SharePoint admin center ->API access once per tenant.
(https://[YourTenant]-admin.sharepoint.com/_layouts/15/online/AdminHome.aspx#/webApiPermissionManagement)

The API access request will appear in the following cases:

1. Customize forms with Modern Forms
2. Add List Actions
3. Deploy solution with Modern Forms or List Actions

After approving the request, you can use it in the Expression Builder -> Context Objects -> User: