It’s ethernet wire (cat5/cat6), but I don’t think this counts as standard use, so you need to figure it out and do the same thing on both ends of this cable.

I’ve also not heard of 24V AC, nor examples of ethernet cable being used for it. My (limited) experience is transmitting DC voltage on ethernet cables. But I’ve also never messed with doorbells, which I do have the impression historically use AC voltage.

I think for anyone to tell more here, we’d need to know what connections you need to make at both ends, what the run length of this wire is, etc.

Might need additional pictures, also. Left third of your collage picture isn’t readable…