Depends if you want an alternate front-end and you can self-host, or you're looking for a third party.

For the former, I generally look at what LibRedirect has as options: https://libredirect.manerakai.com/

Proxigram seems unmaintained, but kittygram seems to be actively developed: https://codeberg.org/irelephant/kittygram

Something to use with a normal web browser that requires no login would be nice. Like Libreddit or Nitter.

Well the description for Kittygram is: "Kittygram is an anonymous, privacy-friendly, lightweight, and open-source Instagram frontend inspired by Nitter."

I don't think it works anymore. Tried various instances out there. Have you used it or found a working one ?

I've never had an Instagram account, and I'm trying to keep it that way.

Most of these front ends need to be stocked with login cookies, that's how they bypass the login wall. If you want to self host a bypass you need to create at least one dummy account on that service.

It's impossible to build a foobar equivalent unless it's literally foobar, because the value of foobar isn't the software, but the fact that other people post stuff there. There's no point having a restaurant menu platform unless you have restaurant menus on it. Have you considered going around your city and taking pictures of restaurant menus, then attaching them to a map?

I've had people send me reels as links to ddinstagram.com and kkinstagram.com, which at least in Telegram, get transformed into a video that can be played inline from the link preview and downloaded.

These "embed fixers" aren't hated by platforms nearly as much as alternative front-ends are.

Yes but they do let you view the content without an account, so that does partially answer the question in the comment I was replying to.