600 V, 5 A, 40 ns — what this diode was built for
That 40 ns trr puts it squarely in the class used for continuous-conduction-mode PFC boost stages, output rectification in flyback converters up to about 150 W, and snubber/clamp circuits where reverse recovery charge needs to stay low. The 2.9 V forward drop at 5 A is a typical trade-off for a fast diode at this voltage class — you get the speed, you pay the Vf. The DO-201AD axial-lead package is a through-hole format common in PTH boards and point-to-point wiring in power supplies and industrial converters.
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Cross-reference hunt — what to look for
A standard fast-recovery diode from ST's own STTH5 series or from competitors like ON Semiconductor's MUR series or Vishay's UF series with the same voltage, current, and trr ratings is the starting point. The 40 ns trr is the tightest constraint — many 600 V 5 A diodes spec 50 ns or 75 ns, which may or may not work depending on the switching frequency and softness requirements of the original design.