Not comparable with instagram yet, but its growing fast https://pixelfed.org/servers . And for my interests it is more Than enough. I am no poweruser and follow only a few people, but if i wanted so, i could browse for hours in my subscription-feed.
There is an opensource Alternative i like called huggingface : https://huggingface.co/chat/ https://github.com/huggingface . You can even try different models and languages.
Edit: Just learned about the existence of lemmynsfw.com. At the moment not compareable but its growing fast.