The PXF filter Pushdown supports the following data types as documented here: About PXF Filter Pushdown
INT2, INT4, INT8 CHAR, TEXT FLOAT NUMERIC (not available with the S3 connector when using S3 Select) BOOL DATE, TIMESTAMP
Using an unsupported data type, such as varchar, for the Pushdown filter can cause issues such as slowness or other issues when accessing the data.