Imagine that in the initial frame of reference, before the rocket begins its constant (linear) acceleration, there is a long line of regularly spaced 'mile posts' spaced 1 light-year apart in the direction of the spaceship's acceleration.
As the spaceship accelerates, the mile posts are observed from the spaceship to have ever increasing speed and ever decreasing spacing (due to length contraction).
Note: while the speed of the mile posts relative to the spaceship is ever increasing, the rate of increase of speed decreases such that relative speed approaches but never reaches $c$.
So, after having accelerated for some time, it can certainly be that 100,000 mile posts have passed by the spaceship after just 12 years have elapsed on the spaceship's clock.
Now, you seem to be concluding from this that, according to those in the spaceship, they have traveled 100,000 light-years in 12 years which implies a speed far greater than $c$.
But remember, due to length contraction, the mile posts are separated by far less than 1 light-year according to the rulers at rest in the spaceship's frame of reference. In other words, according to those in the spaceship, they've covered a distance less than 12 light-years in that 12 years of elapsed time.
From the linked article:
From the ship's frame, the acceleration would continue at the same
rate. However, due to Lorentz contraction, the galaxy around the ship
would appear to become squashed in the direction of travel, and a
destination many light years away would appear to become much closer.
Traveling to this destination at subluminal speeds would become
practical for the onboard travellers. Ultimately, from the ship's
frame, it would be possible to reach anywhere in the observable
universe, without the ship ever accelerating to light speed.