All my photos saved on digikam are subjected to compression. Is there any way to go around this in the program?

This makes serious photo editing somewhat impossible.

see: settings -> configure Digikam -> save images -> jpeg quality

jpeg is still compressed no matter what quality you use.

At least for me, though, it automatically saves all pictures as png. png is a lossless compression format, you lose no quality whatsoever from using png compression. So what is the problem with it?

If, for some reason, you can't even use lossless compression, you can also make it save as tiff. Just change the extension of a file you want to save to .tiff or .tif and it will remember that for future pictures.