How do I do a case insensitive search using a!queryFilter? For example, the valu

Do you use a view? In that case the below procedure could be chosen as one of the alternatives:
          -          Maintain another copy of the column (on which you are searching) in lower case or upper case using the functions in database.
          -          The query filter should be applied on this new column and send the value of the filter as per the case maintained in the new column.
                    a!queryFilter(
                              field: "<field_name>", /*added newly*/
                              operator: "=",
                              value: fn!lower(ri!filterValue_txt) OR fn!upper(ri!filterValue_txt) /*upper or lower functions can be used depending on the case maintained in database*/
                    )

By doing in the above way, AFAIK it could help you retrieve the results in much efficient way and you could also make a direct query instead of writing the rules in Appian to do the work.

Do you use a view? In that case the below procedure could be chosen as one of the alternatives:
          -          Maintain another copy of the column (on which you are searching) in lower case or upper case using the functions in database.
          -          The query filter should be applied on this new column and send the value of the filter as per the case maintained in the new column.
                    a!queryFilter(
                              field: "<field_name>", /*added newly*/
                              operator: "=",
                              value: fn!lower(ri!filterValue_txt) OR fn!upper(ri!filterValue_txt) /*upper or lower functions can be used depending on the case maintained in database*/
                    )

By doing in the above way, AFAIK it could help you retrieve the results in much efficient way and you could also make a direct query instead of writing the rules in Appian to do the work.