Canadarm received a lot of media coverage when it was deployed on ISS. What makes it so special? Is it the fact that it crawls on the outer surface of the ISS to any location is needed? Or is the arm permanently attached to the same spot like a crane

Every piece of tech that goes into space has insane design requirements. Sending stuff is expensive, it has to be extremely lightweight, and absurdly reliable, yet (in this case) it should have the capacity to be repaired with gum and shoelace by a crew member (or expected to “just work” even in case of partial failure, as in case of JWST), so everything has to be impeccably thought-out and produced. There is a lot of info about how space equipment is designed and built, and I find it an interesting read (and recommend everyone interested in designing stuff). I haven't stumbled upon the Canadarm documentary specifically, but I am sure that it has some clever hacks in the design to meet the specs, the production was extremely precise, etc.(*)

For example, I guess that designers had to take into account that the arm's movement also moves the shuttle (counter-force), and adds some angular velocity, which has to be compensated somehow. It moves (carefully puts in orbit?..) heavy satellites - so it must be both precise and strong. Weightlessness means the arm and motors can be light and thin/small, yet it should be reliable as losing control in space means catastrophe. I don't remember any other machinery (17m!) of this size launched into space - there are challenges to solve. The arm was essential for the whole operations of the shuttle - it moved astronauts, and cargo, launched satellites, and enabled in-flight repairs, so, yeah, it's a big deal.

Also: I've read a book, an astronaut's autobiography (I believe it was Mike Mullane's). It was mentioned here (the team was repairing it, or something); but again, no saucy details. The other special thing is that it was made in Canada, which doesn't have much space-related stuff going on. It's kind of national pride (according to the book and this YouTube channel)

Personally I'm surprised by your surprise. Everything in the space is “special” in a sense, what made you ask the question? : )

(*) - just checked, some info exists​;​ but, it's scarse and not very detailed.

but I am sure that it has some clever hacks

In this context I don’t think the word ”hack” is the appropriate one. Using hacks while building a piece of technology is considered poor design. You should use the expression ingenious solution or something else instead

Okay