Advice with strange malfunction of my 3D printouts

Hi, I'm new on this forum, and I have a problem that disturbs me for over two weeks. I have factory new Creality CR 20 pro for 2 months. I've started using my printer by buying PLA from a trusted store and printing some basic parts. Two weeks ago I bought PET-G and I started testing this new material. At the beginning I printed small gears, and I was not happy enough with the quality of this parts. I started testing new functions in Cura and after few unsuccessful printouts I found the best settings for the gears parts. I thought I finally learnt how to use my 3d printer but then I proceeded to printing something different than gears. I had to print something not circular like gears but with rectangular walls, and sharp edges. I noticed that every single part had corners a little slightly pulled forward than walls, and walls were slightly concave. For example, I printed the basic part like calibration cube and during this ,considerably easy to print part, I noticed concave walls. At first I thought my new, very much modified Cura settings can cause this problem, but then I used default Cura settings and the printout had the same defect as previous. So I thought it could be a type of the material that I used. So I changed PET-G to PLA which is considered easier to print than PET-G. Unfortunately, I had the same flaw as previous parts. I noticed that PLA had less visible defect than PET-G but it was still unacceptable. For two weeks I haven't came up with an idea why this problem occurs and I run out of ideas how can I fix it. Could You help me with this frustrating problem? I attached some photos (gray parts are made of PET-G, white of PLA).