Problem with ADC of stm32G474RET6

[Mshakiba]

I am running the ADC using a timer trigger and DMA to sample a sinusoidal signal.
The captured samples are transmitted to a PC via UART.
However, as shown in the attached image, the ADC output appears to be step-like and does not capture smoothly changing values, even though the input signal is a clean sine wave.
I have checked the external reference voltage, interrupts, and the microcontroller power supply, but the issue still persist

 

[TDK]

Are you calibrating the ADC on startup? This is mandatory.

Are there appropriate decoupling caps next to the VREF+ pin?

Consider sharing the schematic if you can.