Hello Jan,
Please, be sure to select the correct voltage reference for DAC. According to K60's reference manual, you can chose between two different Voltage Reference: Internal reference that is obtained from VREF_OUT and External Reference that is obtained from VDDA.
I made a simple example using PEx and selected the External Reference and DAC is working without problems. (For Internal reference, you will need to configure VREF)

I attach this basic example,
Hope this can help you,
Best Regards,
Isaac
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