https://imginn.com/ - for content from Instagram. Won't let you view private accounts obviously, but current for non-private accounts.

https://xcancel.com/ - (a Nitter instance) for content from Twitter. Same deal, can't view private accounts, but anything else goes.

https://coomer.st/ - for OnlyFans/Fansly content.

https://kemono.cr/ - for Patreon/Pixiv/Discord/etc content.

https://github.com/Emy69/CoomerDL - bulk downloader for Coomer/Kemono and others

Not sure for Pinterest.

Anyway, just because they're "private" in the sense that you're not using any of the major corporations servers, they're not private in the sense that the admins of these sites won't see your IP. Still consider using a VPN while using these for more actual privacy.

There is nitter.net for twitter, but I dont have any other alternatives.

Remember that you can just not using them ;)

I was a bit confused as to what you meant; image browsing apps to me are things like EOG/Loupe, Gwenview, or whatever Apple/Microsoft use for that now. So you're looking for a social media platform for sharing images, not software for browsing images? What is thirst content?