Time "freezes" in the POV of an observer moving with the velocity c - how can it be affected by other objects?

I'm quite a newbie to "relative" physics, so please excuse me if this question seems obvious or stupid. Also I'm writing on my phone, so there will be one or another mistakes.

I red that for an observer moving at the speed of light time comes to a full stop (for the observer). Therefore I assume that this observer couldn't observe any changes in the outside world; is this correct?

Given that my previous assumption is true, how can outside objects interact with the observer (light)? For example, imagine a light particle being emitted by the sun. AFAIK there are no major gravity fields nearby, so it should travel in a straight line. At the time of its emission there are no objects in this line, but during its travel another object with a velocity < c moves in front of the observer. Because time stopped in the observers POV it shouldn't be aware of this object blocking the path.

Is this assumption correct (or rather, what is wrong about it)? I can more or less understand how two objects can have different timescales, but I can't wrap my head around the scale of 0.

Every explanation or link to recources (which can be understood by a high school student) is appreciated.