The short answer

Yes, but limit it — spinach is high in oxalates.

Why

Spinach is nutritious, but it contains oxalic acid, which binds to calcium and can reduce how much a budgie absorbs. For a small bird that needs good calcium levels, spinach is best offered occasionally rather than daily.

How to feed it

Offer a small piece of washed raw leaf now and then, and rotate it with lower-oxalate greens like kale.

How much & how often

A couple of times a week at most.