Usually the project author is located under the @project_author
, however, you can use the following expression to extract the initials of the project author, and it should be applied without a problem if you replace @project_author
with @user_full_name
. But in this example, I am using @project_author
. Please make sure to adjust the start and length of the substr(string,start[,length])
based on string that you have.
@project_author || ': ' || '(' || substr(@project_author, 1,1) || substr(@project_author, 7,1) || ')'
Here is the input in expression:

Here is the output:

Update
If you want the initials to be created automatically, you need to create a custom function for it. You can use the following function to create the initials:
from qgis.core import *
from qgis.gui import *
@qgsfunction(args='auto', group='Custom')
def nameInitial(text_field, feature, parent):
split_text = text_field.split()
initial = [nm[0] for nm in split_text]
joinNM = "".join(initial)
return joinNM

Then from Custom functions select the function the you created (nameInitial in this example) and @project_author
.

The output is same as the above but without user adjustment:
@project_author || ': ' || '(' || nameInitial(@project_author ) || ')'
