Thank you for your time on the call today. As per our discussion you had on-premises environment earlier with Entra connect to sync users to Entra ID.
Now, you have decommissioned on-premises environment and move entirely to cloud.
After moving completely to Entra ID you users to change there password by using Entra password policy.
You were unable to do this because initially on-premises AD was handling the password policy.
To fix this issue, you changed "passwordneverexpires" to "false" in office admin portal GUI. This helped all Entra ID created users to change their password now.
And you changed "passwordneverexpires" to "false" using PowerShell commands in below article. This helped all synced users to change their password now.
Please "Accept the answer" if the information helped you. This will help us and others in the community as well.