is it bug?

Not exactly, it was previously decided to not handle this.

Objects that are not primitives should generally not be used like this. You are causing an implicit string conversion which the compiler will ignore for non-state variables. Instead of treating every value in the template as potentially dynamic, only property accesses and function calls will add an effect.

Usually the implicit string conversion of objects is fairly useless anyway (e.g. with dates it outputs a very verbose representation and for arrays there are no spaces between elements). If you want this to happen and dynamically update anyway, you can explicitly convert the value:

- <p>value #1: {newValue}</p>
+ <p>value #1: {newValue.toString()}</p>

Playground

You can also make the variable be considered stateful, e.g.:

- let { value: newValue } = value;
+ let { value: newValue } = $derived(value);

Playground
(Of course this will update the variable in case the $derived is triggered.)

Thanks, I understood