I have never seen an Instagram ad on my phone using both the Android and iOS apps. I don't know why, but there are certain accounts that have ads disabled (I'm not the only one [0]). I guess I just got lucky. My alternate accounts all get ads like normal. I don't think I would use Instagram if I got ads like my friends do.
[0] https://www.fastcompany.com/90166955/i-have-a-secret-ad-free...