PostgreSQL "cursor is not positioned on a row" with ODBC driver - c++

Question

I'm trying to use on PostgreSQL 12.2 an updatable cursor inside transaction using the ODBC driver (ANSI 12.1) and C++.
If I declare the cursor with SQLSetCursorName and SQLPrepare + SQLExecute for the query in one statement, and the update in other statement it gives the SQLSTATE 24000 and message cursor "cur0" is not positioned on a row.
If the update is made in the same statement, it gives the SQLSTATE 24000 and message Invalid cursor state.
On the DSN I've checked Use Declare/Fetch, set the Level of rollback on errors option to Statement, and unchecked Updatable Cursors, following what is in https://www.microfocus.com/documentation/enterprise-developer/ed40pu15/ED-VS2015/GUID-1F1C4505-B771-4F8E-B274-952CAF3E8265.html.
The only way possible was with SQLSetPos, but using the same statement for the SELECT and the UPDATE, as described in http://micronetinternational.com/index.pl/en/00/https/www.postgresql-archive.org/ERROR-with-quot-Update-where-Current-of-quot-td4499184.html.
Using DBeaver, which uses a JDBC driver, it works normally.
Is it possible to make the update with a different update statement on PostgreSQL using the ODBC driver?
rc = SQLAllocHandle(SQL_HANDLE_ENV, SQL_NULL_HANDLE, &henv);
check_rc(henv, hdbc, hstmt, rc);
rc = SQLSetEnvAttr(henv, SQL_ATTR_ODBC_VERSION, (SQLPOINTER*)SQL_OV_ODBC3, 0);
check_rc(henv, hdbc, hstmt, rc);
rc = SQLAllocHandle(SQL_HANDLE_DBC, henv, &hdbc);
check_rc(henv, hdbc, hstmt, rc);
rc = lpfSqlConnect(hdbc, (SQLCHAR*)"mydsn", SQL_NTS, (SQLCHAR*)"user", SQL_NTS, (SQLCHAR*)"pass", SQL_NTS);
check_rc(henv, hdbc, hstmt, rc);
rc = SQLSetConnectAttr(hdbc, SQL_ATTR_AUTOCOMMIT, (SQLPOINTER)SQL_AUTOCOMMIT_OFF, SQL_IS_INTEGER);
check_rc(henv, hdbc, hstmt, rc);
rc = SQLAllocHandle(SQL_HANDLE_STMT, hdbc, &hstmt);
check_rc(henv, hdbc, hstmt, rc);
rc = SQLSetStmtAttr(hstmt, SQL_ATTR_NOSCAN, (SQLPOINTER)SQL_NOSCAN_ON, SQL_IS_INTEGER);
check_rc(henv, hdbc, hstmt, rc);
rc = SQLSetStmtAttr(hstmt, SQL_ATTR_CURSOR_TYPE, (void *)SQL_CURSOR_KEYSET_DRIVEN, 0);
check_rc(henv, hdbc, hstmt, rc);
rc = SQLSetStmtAttr(hstmt, SQL_ATTR_CONCURRENCY, (SQLPOINTER)SQL_CONCUR_ROWVER, 0);
check_rc(henv, hdbc, hstmt, rc);
rc = SQLSetCursorName(hstmt, (SQLCHAR *)"cur0", SQL_NTS);
check_rc(henv, hdbc, hstmt, rc);
rc = SQLPrepare(hstmt, (SQLCHAR *)"select field1, field2 from mytable", SQL_NTS);
check_rc(henv, hdbc, hstmt, rc);
rc = SQLExecute(hstmt);
check_rc(henv, hdbc, hstmt, rc);
SQLSMALLINT iNumCols = 0;
rc = SQLNumResultCols(hstmt, &iNumCols);
check_rc(henv, hdbc, hstmt, rc);
for(i = 0; i < iNumCols; ++i)
{
rc = SQLBindCol(hstmt, i + 1, SQL_C_CHAR, data[i], collen[i], &outlen[i]);
check_rc(henv, hdbc, hstmt, rc);
}
for (i = 0; i < 4; ++i)
{
rc = SQLFetch(hstmt);
check_rc(henv, hdbc, hstmt, rc);
}
//////////////////////////////////////////////////////////////////
//it returns SQL_ERROR, SQLSTATE=24000, message "[Microsoft][ODBC Driver Manager] Invalid cursor state"
rc = SQLExecDirect(hstmt, (SQLCHAR *)"UPDATE mytable SET field3 = 'newvalue' where current of cur0", SQL_NTS);
check_rc(henv, hdbc, hstmt, rc);
/////////////////////////////////////////////////////////////////
//or
SQLHSTMT hstmt2 = SQL_NULL_HSTMT; // Statement Handle
rc = SQLAllocHandle(SQL_HANDLE_STMT, hdbc, &hstmt2);
check_rc(henv, hdbc, hstmt2, rc);
rc = SQLSetStmtAttr(hstmt2, SQL_ATTR_RETRIEVE_DATA, (SQLPOINTER)SQL_RD_OFF, SQL_IS_INTEGER);
check_rc(henv, hdbc, hstmt2, rc);
//it returns SQL_ERROR, SQLSTATE=24000, message ERROR: cursor "cur0" is not positioned on a row;
rc = SQLExecDirect(hstmt2, (SQLCHAR *)"UPDATE mytable SET field3 = 'newvalue' where current of cur0", SQL_NTS);
check_rc(henv, hdbc, hstmt2, rc);
////////////////////////////////////////////////////////////
rc = SQLEndTran(SQL_HANDLE_DBC, hdbc, SQL_COMMIT);
check_rc(henv, hdbc, NULL, rc);
rc = SQLSetConnectAttr(hdbc, SQL_ATTR_AUTOCOMMIT, (SQLPOINTER)SQL_AUTOCOMMIT_ON, SQL_IS_INTEGER);
check_rc(henv, hdbc, hstmt, rc);