The Add Join tool should warn the user if the join table has a definition query, since the definition query will be applied to the join.

For example, if we're using a map that someone else created, we might not be aware that the join table has a definition query. And so the definition query would be applied unknowingly.
Edit:
I suppose the GP tool could be enhanced so that the definition query is shown as an editable SQL expression text box right in the tool. We’d have the option of changing the definition query or removing it, if needed (in the join, not the underlying table). Or we could even add a new definition query, if there wasn’t one already.
That would have the added benefit of making it abundantly clear that there is a definition query. It would be hard to ignore. Whereas a small yellow exclamation mark beside a field is easy to accidentally overlook, especially when we see those exclamation points regularly for things like “no index” warnings.
ArcGIS Pro 3.0.3