Hi,
It’s the same on Mallorca as here on Costa del Sol where I live. Most of the rental apartments are furnished but not all. But do not rent anything from abroad it is to easy to get fooled. Book a week or two on a cheap hostel while you look for a nice apartment. It’s the only way to figure out if you like the neighbourhood, neighbours, apartment and to see if the infrastructure fit your needs.
I have many friends who have been fooled by nice e-mailed pictures and low prices, better use your own eyes and talk to the people in the areas that are of interest for you.
Best regards from a sunny Spain