What Sun does in a chart
Sun is the part of the chart that answers one question:Who am I when I feel most like myself? It describes core identity — not events, and not outcomes.
What Aquarius does to it
Aquarius is a air sign, so it moves on ideas and conversation. It is also fixed, which means it holds things. Put those together with Sun and you get identity through independence — independent, systemic, odd-angled, applied specifically to core identity.
Aquarius is ruled by Uranus, so this placement tends to be coloured by independence as well.
The useful version
Placements are not verdicts. This one describes a default setting, not a limit — the things listed above are what you do when you are not thinking about it, which is exactly why noticing them is worth something.