Are there tags to specify that a language is for fiction the asker is writing as opposed to an "official" language (esperanto for example)?
Such conlangs are sometimes called "artlangs" - we don't have a tag for that currently, but it could be appropriate.
The design-goals tag could also be appropriate, depending on the question.
In addition to what curiousdannii mentioned, it should be noted that we currently have specific tags for established conlangs (e.g., esperanto, lojban, toki-pona,tolkien-elvish, etc.) rather than having a separate tag for questions that are relevant to a user's own conlanging. Those questions can be far more varied than questions about popular existing conlangs and should be tagged for other properties of the question (e.g., using design-goals for questions regarding how to achieve particular purposes in one's own conlang, using naturalism for questions about whether features one plans on including in one's conlang are naturalistic, etc.).