Does Instagram reduce the photo quality ?

I know Instagram always reduces the quality of DSLR photos a bit, but when I post a singular photo the quality remains alright, and when I add multiple photos to one post the quality seems to go down. Is there any way to avoid this?

Same situation with me. I guess you can't expect to upload high-resolution images without minimal noise in a photo, else Instagram would be hella laggy for everyone's usage just to load that feed up.
However, there are tutorials on youtube to export high-quality images on to Instagram. But to a certain extent.

yes they are always reduced, just like facebook

Video quality is generally much more significantly impacted compared to pictures. But both get hit