I'm in the ultra minority, but I use https://instagram.com on my phone and I've never seen an ad.
[0] https://www.fastcompany.com/90166955/i-have-a-secret-ad-free...
Edit: I had assumed the trick was using the mobile website, since I used to see ads when I used the Android app.
"Facebook adds 5 divs, 9 spans and 30 css classes to every single post in the timeline to make it more difficult to identify and block 'Sponsored' posts, oh my."