Use the Split and Concat functions to extract the initials from the user's full name. If the user’s name is "John Doe", the initials would be "JD".
Concat(Split(User().FullName, " "), Left(Result, 1))
Combine these initials with other components to form the unique ID. For example, if the Change Request type is "ORG", the SharePoint ID is "0005", and the initials are "JD", the unique ID would be "ORG-0005-JD".
"ORG-" & SharePointID & "-" & Concat(Split(User().FullName, " "), Left(Result, 1))
Let me know if this helps.
Ref:
https://powerusers.microsoft.com/t5/Building-Power-Apps/How-to-get-users-initals-into-a-label/td-p/44939
https://powerusers.microsoft.com/t5/Building-Power-Apps/Unique-ID-based-on-initials-of-their-name/td-p/1199635