Image quality can be affected by a variety of factors, including using a low-resolution file or heavy compression. Make sure you use a high-resolution file and minimize compression.
After uploading, it is difficult to improve the image quality because Instagram automatically applies compression. Therefore, it is best to get the best possible image quality before uploading.
There are many image editing software options including Adobe Photoshop, GIMP, and Canva. Choose the software you are most familiar with and that best meets your needs.
Yes, I also often sit on Instagram, and now I also work. Sometimes there are problems with vector images. But I found https://depositphotos.com/vectors/lake.html a site where there is a large database of multi-thematic images. They help me in my work.