Try filtering items property of gallery control on "BrowseScreen" to something like:

Filter(DataSource, 'Created By'.Email = User().Email) 

Where DataSource is your SharePoint list data source.

Try filtering items property of gallery control on "BrowseScreen" to something like:

Filter(DataSource, 'Created By'.Email = User().Email) 

Where DataSource is your SharePoint list data source.

Update from comments:

SortByColumns(Filter([@'Template'], 'Created By'.Email = User().Email && StartsWith('Purpose and objectives', TextSearchBox1.Text)), "Title", If(SortDescending1, Descending, Ascending))