The value of standard electrode potential for the oxidation of Cl? ions is more positive than that of water, even then in the electrolysis of aqueous sodium chloride, why are Cl? ions oxidized at the anode instead of water?

It is depending on concentration cCl- >>>>OH- in aqueous solution, and on the Anode material. The reaction is also exergonic. Needs Power to get it.
Additional the overvoltage for developing oxygen is higher as for chlorine.
Some can find here

https://www.quora.com/During-NaCl-electrolysis-why-is-chlorine-gas-liberated-Shouldnt-it-be-oxygen-gas-O2-2-H2O-4-e-4-OH-E-0-503-at-ph-7-vs-Cl2-2e-2Cl-E-1-36

Quote from: aarna on September 02, 2022, 11:12:18 AM
The value of standard electrode potential for the oxidation of Cl? ions is more positive than that of water, even then in the electrolysis of aqueous sodium chloride, why are Cl? ions oxidized at the anode instead of water?

The Effect of Overvoltage in the electrolysis of NaCl- Because of overvoltage, the anode reaction of this cell is the oxidation of Cl- to Cl₂ gas rather than the oxidation of water to H⁺ and O₂ gas.
In order to predict the product of the electrolysis, we consider the two possible oxidation half-reactions and the two possible reduction half-reactions:
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Since the oxidation of water has a less  negative electrode potential than the oxidation of Cl-, we would initial-ly predict that it would be easier to remove electrons from water, and thus water should be oxidized at the
anode. Similarly, since the reduction of water has a more positive electrode potential than the reduction of Na+, we would expect that it would be easier to get water to accept electrons, so water should be reduced at the cathode. In other words, we initially predict that a sodium chloride solution would simply result in the lec-trolysis of water, producing oxygen gas at the anode and hydrogen gas at the cathode. If we construct such a cell, however, we find that, although hydrogen gas is indeed formed at the cathode (as predicted), oxygen gas is not formed at the anode?chlorine gas is formed instead. Why? The answer is that even though the electrode potential for the oxidation of water is -0.82 V, the reaction actually requires a voltage greater than 0.82 V in order to occur.
This additional voltage, the overvoltage, increases the voltage required for the oxidation of water to about 1.4 V. The result is that the chloride ion oxidizes more easily than water and Cl₂(g) is observed at the anode.
The oxidation of Cl⁻(aq) is much more rapid than the oxidation of H2O.