可以 bytes 转换上传会转为 BLOB；或者自己指定一下类型，参考:

import dolphindb.settings as keys

df.__DolphinDB_Type__ = {
    'cint': keys.DT_INT,
    'csymbol': keys.DT_SYMBOL,
    'cblob': keys.DT_BLOB,
}

s.upload({"df_true": df})
print(s.run("schema(df_true)")['colDefs'])

https://github.com/dolphindb/api_python3/blob/master/README_CN_NEW/3_AdvancedOperations/3.1_DataTypeCasting/3.1.1_PROTOCOL_DDB.md