Hi @Sormick ,
To focus the excel file use Focus window action as mentioned below.
I have created the similar flow.Please find the solution

Code:
Folder.GetFiles Folder: $'''C:\\Users\\OneDrive\\Desktop\\Power Automate Desktop\\Projects\\BOM Costing\\Templates''' FileFilter: $'''*''' IncludeSubfolders: False FailOnAccessDenied: True SortBy1: Folder.SortBy.NoSort SortDescending1: False SortBy2: Folder.SortBy.NoSort SortDescending2: False SortBy3: Folder.SortBy.NoSort SortDescending3: False Files=> Files
LOOP FOREACH CurrentItem IN Files
SET ToFocusFileName TO $'''%CurrentItem.NameWithoutExtension% - Excel'''
Text.Trim Text: ToFocusFileName TrimOption: Text.TrimOption.Both TrimmedText=> ToFocusFileName
Excel.LaunchExcel.LaunchAndOpenUnderExistingProcess Path: CurrentItem.FullName Visible: True ReadOnly: False Instance=> ExcelInstance
WAIT 2
UIAutomation.FocusWindow.FocusByTitleClass Title: ToFocusFileName Class: $'''XLMAIN'''
END
(Note:- if you got your solution you can mark as solution and gives kudos)
Thanks & Regards
Vishnu Reddy