Hi Mussienko! Great question. I did a very long post years ago on how to photograph oil paintings without any glare. I start with using a smart phone and editing in Photoshop or Lightroom then I move on to a dual polarization setup that magically wipes away the glare. Recently I took a few photos of larger paintings with a DSLR using overcast light coming through a doorway and that worked really well but the light has to be just right and waiting for those days doesn't work most of the time. Here is the post. https://chrisbeaven.com/art-tips/professional-photos-of-an-oil-painting-without-glare/ Let me know if the post is helpful or if you have any more questions.

I don't know if this can be called advice but when i take my photos, I take them in two different light settings. I try to set them in a way so that later on I can combine the two photos on photoshop and avoid glare. Though I haven't found a way to take a photo with no glare at all.