In astrological tradition, the Sun governs core identity and the sense of self, while Libra is a air sign read as fair-minded, diplomatic, aesthetic, and partnership-oriented.
So Sun in Libra is often read as a placement where how someone shines and seeks to be recognized takes on a fair-minded, diplomatic quality. Tradition holds that someone with this placement tends to expresses its vitality in a way that feels aesthetic — coloured by the air-sign temperament of Libra rather than by any single rule.
None of this is a prediction or a fixed trait. These are tendencies astrologers have long associated with Sun in Libra, and how they actually show up depends on the rest of the chart — the houses, the aspects, and the other placements that this guide cannot see.
A general guide to astrological tradition — tendencies, not predictions. It describes the placement in the abstract and is not about any specific person.