I am sorry that I am answering my own question, but I didn’t find an answer right away when I was searching, so I decided to share it here right after I figured it out myself. Because I am pretty sure that I am not the first or last one who was searching.
By default, if you export to apng, the resulting file will play only once.
To export to apng, you need to open the Export panel, then go to Advanced tab. Choose apng both on Video and Codec tabs. The last crucial step to make an infinite loop is to visit also the Other tab and enter into the textbox plays=0. This will make animation cycle indefinitely.
If you want animation to cycle some finite number of times, just enter that amount instead of 0.