If the bad semester is an isolated period and the rest of the transcript recovered, you usually do not need to turn the application into an explanation of the setback unless there is a place specifically asking for context.

If the drop is large enough that a recruiter is likely to notice it, a brief factual explanation can help when the application provides an optional-information section. Keep it short and focus on the recovery rather than the circumstances.

Do not over-defend the grades. The strongest signal is the evidence afterward that the semester was not representative of your normal performance. If useful, this guide on consulting applications with a lower GPA gives more detail.

If it's one semester and you bounced back, transcript already tells part of story imo.

I would only explain if there's optional box or drop is really obvious.