Is Location a choice field, If Yes, the use below formula -
SortByColumns(Filter(AddColumns([@'engineering Inventory'],"LocationCustom", Location.Value), StartsWith(Title, TextSearchBox1.Text) || StartsWith(LocationCustom,TextSearchBox1.Text)), "Title", If(SortDescending1, Descending, Ascending))
If Location is pf type Single line of text, then try below (made some changes in syntax) -
SortByColumns(Filter([@'engineering Inventory'], StartsWith(Title, TextSearchBox1.Text) || StartsWith(Location,TextSearchBox1.Text)), "Title", If(SortDescending1, Descending, Ascending))