You can use the starts-with expression
This is case insensitive. Combine it with length for a (case insensitive) exact match.
Another option, if you don't want slow searches, would be to add another column in your database where you save an all lowercase or uppercase version of your data, and then use that to search. This has its own set of issues though (duplicate data, needing to always use search fields for columns you're not showing, etc.)
If it’s not an issue, instead of using xpath as datasource you might try microflow datasource and implement retrieve list + filter by expression list operation (convert to lowercase/uppercase)