Short answer: 28 V DC max in normal operation; 30 V absolute maximum on the IC. Do not design to the absolute maximum.
Details
Controller limit (datasheet):
U1 TPS54331DR VIN operating range: 3.5 V to 28 V. Absolute max VIN: 30 V.
Freewheel diode:
D1 PDS760-13 reverse-voltage rating (VRRM): 60 V, so it is not the limiting part.
Board-level limit depends on the lowest-rated VIN-connected part:
Input caps C1, C2, and small VIN cap C7, plus the input connector J1. Their voltage ratings aren’t specified in the current BOM, so the safe max input is the minimum of their ratings and the IC’s 28 V operating limit.
If you tell me your intended max VIN (e.g., 12 V, 24 V), I can set the capacitor and connector ratings accordingly and update the design.
This project appears to be a power supply circuit using the TPS54331 step-down (Buck) converter from Texas Instruments. The target output voltage is 3.3V. It also features electromagnetic interference (EMI) mitigation components such as an inductor, capacitors and a diode. An LED is included for indication purposes. #Buck#TPS54331#project