I agree with nhooyr's analysis. The interface{} will anyway transparently "contain" a pointer-to-the-[]byte, in other words, the []byte value itself will be heap allocated.
(Note for anyone new to this that the "[]byte-value" - we say "the byte slice" - is a distinct thing from the "values stored-in-the-byte-slice", which is a heap allocated backing array)
(Note for anyone new to this that the "[]byte-value" - we say "the byte slice" - is a distinct thing from the "values stored-in-the-byte-slice", which is a heap allocated backing array)