I'm trying to make a Formula column that will display the full name from a Notes column where I type in their username.
See screenshot example:


Basically, "Notes" column is a place to add points of contact users but aren't assigned to or are reporters of the issue, so we use the Notes column and map it to the Formula column to display their name. Then the ultimate goal would be to Group by Formula. Is there something wrong with how my formula is written?
This is a test example, so "usera" is the username with "User A" is their full name. Same for "userb"
EDIT: also adding that "usera" and "userb" are active users