Hi @Sid_Works ,
Hope you are doing well!
I believe you are trying this way:

Then once double layout is selected, then have the below property set

Then once done with above setting, the formula on item property of combo box should be as below:
Office365Users.SearchUser({searchTerm:Self.SearchText})
And with this once you select any user, while search you will get both DisplayName and Email address of user, however when you select the user, it will only show DisplayName of user and I believe you are looking like below format:
USER1 (USER1@abc.com), if yes then try below code on item property of combo box:
AddColumns(
Office365Users.SearchUser({searchTerm: Self.SearchText}),
"NAME",
Concatenate(
DisplayName,
"(",
Mail,
")"
)
)
And also make sure to select "NAME" in Primary text as below:

I hope this helps.
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Thanks,
ANB