An honest answer: the list of people who liked a post is no longer public. Here is what that means and what is still available.
There was a time when the full list of people who liked a post was visible to anyone who opened it. Instagram closed that, and today only the author sees who liked their own posts. The count is public, the names are not. That is a decision made on Instagram's side, not a technical puzzle waiting to be solved, so any site promising to reveal the list of likers of somebody else's post is either showing you invented names or collecting your login details. Both are worth walking away from.
How many people liked a post is public and comes with the post itself.
For posts on your own account the list is right there in the app — no third party needed, and none should be trusted with your password.
The photo, video or carousel behind those likes can be saved in original quality. Paste the post link above.