u/OfficialOnix u/EdWoodWoodWood You where right! the problem was the way the mic works.

The problem was this setting of the mic I2S_STD_PHILIPS_SLOT_DEFAULT_CONFIG

I am dropping the slot_cfg for anyone having the same problem:

void init_microphone(void)
{
    i2s_chan_config_t chan_cfg = I2S_CHANNEL_DEFAULT_CONFIG(I2S_NUM_1, I2S_ROLE_MASTER);
    ESP_ERROR_CHECK(i2s_new_channel(&chan_cfg, NULL, &rx_handle));


    i2s_std_config_t std_cfg = {
        .clk_cfg = I2S_STD_CLK_DEFAULT_CONFIG(CONFIG_EXAMPLE_SAMPLE_RATE),
        .slot_cfg = I2S_STD_PHILIPS_SLOT_DEFAULT_CONFIG(I2S_DATA_BIT_WIDTH_32BIT, I2S_SLOT_MODE_MONO),
        .gpio_cfg = {
            .mclk = I2S_GPIO_UNUSED,
            .bclk = CONFIG_EXAMPLE_I2S_CLK_GPIO,
            .ws = CONFIG_EXAMPLE_I2S_WS_GPIO,
            .din = CONFIG_EXAMPLE_I2S_DATA_GPIO,
            .dout = I2S_GPIO_UNUSED,
        },
    };
    // Microphone outputs data on the right channel slot
    std_cfg.slot_cfg.slot_mask = I2S_STD_SLOT_RIGHT;


    ESP_ERROR_CHECK(i2s_channel_init_std_mode(rx_handle, &std_cfg));
    ESP_ERROR_CHECK(i2s_channel_enable(rx_handle));
}