My 2 dental implants are now ready for crowns by general dentist. in general, is it more complicated to install an implant than to place its crowns?

Procedures: The procedures are different and require different skill sets. Additionally, your occlusion, the positions of the implants, lines of draw, contours of the restorations, and so many factors will contribute to degree of difficulty. As no two people are alike, this is a question to be asked of your Dentist.

Both: Placing dental implant fixtures can be relatively simple to place depending upon many factors such as type, width and height of bone as well as adjacent tooth proximity and angulation. Similarly, fabricating a crown can be relatively simple or very complex based upon amount and integrity of tooth structure, occlusion, inter-jaw space etc. There is no simple general answer to your question.

Crowns Are Easier: In general, getting the crowns should be easier for you. You won't have to get numb, and there will be no invasive work done. It's simply an impression or two, a check of the bite, and perhaps a few photos. Then all the custom pieces are made in a lab and placed into the implants...either screwed or cemented into place. For the dentists, however, implants and crowns can be equally challenging.