12th House Libra Sun here (conjunct Mars, and at the apex of a T-Square with a 9th House Cancer Jupiter and a 3rd House Capricorn Saturn/Uranus/Neptune). Yikes, I know.
I've always had a strange relationship with my "ego" -- I feel like for most of my life, I've either underestimated or overestimated myself, probably because of this 12th House nebulousness. The underestimating comes more in group activities ("you can take the last shot"), whereas the overestimating comes in solitude ("I'm meant to do something special"), which is where most 12th House Suns seem to gain clarity.
But this T-Square configuration has given me a ton of 12th House Energy and I'm still figuring out how to best utilize it, to some extent. My natural tendency is to sacrifice myself in groups/teams, not necessarily to gain recognition for "selflessness" (at least not consciously), but more because I'm actually uncomfortable with the spotlight, and because I assume that most other people don't want to sacrifice their wants/needs. But this might qualify as a "martyr complex," who knows.
Meditating and letting go has been the best way to deal with this energy. But during tougher times, self-medicating via alcohol etc. has been a negative way of addressing this. I also feel like I experienced an ego death around 19, but have had to "build" an ego in the decade following that, to be able to support myself in a dog-eat-dog world.
My dad was definitely a 12th H figure. My parents split when I was 5 and he was the world-traveling, kind and cultured one...but I didn't see him much after the divorce, and we never shared many deeper feelings. I started to shed my idealized picture of him in my teens though. The fact that my Sun is in hard aspect to 6 planets via Conjunction or Square makes it very difficult to put "who I am" into a box. Sometimes my Jupiter/Uranus is activated with my Sun/Mars and I become a confident risk-taker...but then there are times where my Saturn/Neptune are activated, and I'd rather work alone and disappear from the outside world.
[edit] The morph-into-who-people-want-me-to-be theme mentioned in this thread has definitely applied to me, with my Libra energy only adding fuel to that. A part of me knows that prioritizing some form of spirituality is going to be the best thing that I can do for my own mental health, but for some reason it's hard to let go completely.
My immediate family is also all 1st or 10th House Suns so they don't understand why it's so hard for me to turn my strengths into their external definition of "success."