Jeff-Relf.Me @. writes:

We can't see Sgr A* PROPER, directly, and you need
INFINITE precision to measure a TRUE singularity.

Doesn't matter, it's the size of the event horizon that counts, not
the singularity. As long as there is enough mass inside an event horizon
there is a black hole, even if there is weird physics unknown to us
inside that prevents formation of a singularity. We can never know what
happens inside an event horizon.

We see that Sgr A* is there, not by seeing it, but by tracking stars
that are orbiting it.

https://en.wikipedia.org/wiki/S0%E2%80%93102
https://en.wikipedia.org/wiki/S2_(star)
amongst others