You have an MSOL user to match with its Active Directory (AD) object
Your alias changes in your AD is not occur in Admin Center
You are having issue following DirSync soft matching found in Microsoft articles
Steps
AAD Connect (DirSync) Soft-Matching is another word for SMTP matching. In addition, it is a steps to match on-premises user accounts to Office 365 user accounts for AD sync
In this example, we will use the made up object below to apply AAD Connect (DirSync) Soft-Matching steps.
dnunez@weeplaygames.xyz (Msol Cloud object)
Donna.nunez@weeplaygames.xyz (On-prem AD object)
Firstly, you will have to enable AD Users and Computer (ADUC) advance feature.
Go to your On-Prem AD > ADUC
View Tab> Advance Features should be checked
After that, locate to the target users account
Right Click > Properties
After that, apply or confirm below details in the Account & Attribute Editor tab.
Go to account tab
After that, change user logon name to the cloud UPN
Click on Attribute Editor
After that, change the following
Mail to dnunez@weeplaygames.xyz (Cloud)
userPrincipalName to dnunez@weeplaygames.xyz (Cloud)
proxyAddress to SMTP:dnunez@weeplaygames.xyz (Cloud)
Target address to dnunez@weeplaygames.xyz (Cloud)
Note: SMTP is the primary
Lastly, you will have to confirm the changes and force an Azure AD (AAD) connect sync.
Click OK and Apply
After that, run Delta Sync
On your AD server
Open a PowerShell session
Type in: Start-ADSyncSyncCycle -Policytype Delta
Check Synchronization Service > Exported (onmicrosoft.com) > Updates
Lastly, ensure that 0 minute is showing as last sync time. On admin center > Home > DirSync Status card