Is there some resource of non-tactical positions to practice analysing? In point 3 of this answer RemcoGerlich implies that a good way to improve, for a class player, would be to develop the skill of “[taking] any position and [figuring] out what’s going on”.

It seems to me this is the kind of observation that has been made quite often before. Is there any kind of resource that provides a collection of positions for this purpose? Preferably ordered by difficulty and with some annotations to check your own analysis against.

Clearly, there are books about the middlegame but the ones that I know talk about various topics in isolation (providing positions which revolve solely around the topic of that chapter) and not about general analysis. (Not that I would like such a collection of positions to only include middlegame positions but this example comes the closest to what I have in mind.)

I am also not looking for tactical puzzles. There are plenty of books and apps that provide them. In case of a tactical puzzle it’s very clear what’s going on in the position: there’s an immediately winning tactic. (Or sometimes a single drawing move. But mostly it’s clearly one or the other.)

Annotated games could possibly be used for this, but it’s not trivial to select the positions that would be of interest for this without reading the annotations. Also, the strategical themes wouldn’t change so often during a single game so the amount of practice positions derived from an annotated game is quite low relative to the effort required to find them – clearly a selection by a renowned chess teacher would be far superior.

Ideally, I’m looking for a collection of positions that are decidedly not tactical and that have various strategical themes in them so the reader may analyse and evaluate the position, afterwards checking with the provided annotations. They don’t need to have a clear best move, it would be enough to just try and find all important themes and get a good sense of which side is better.
I looked at my library, and opened up a number of books. The old Dvoretsky books really do not do this much, but the "School of Future Champions" and "School of Chess Excellence" series do have many sections that just say "white (or black) to play", and nothing more.

Other Dvoretsky books that do that significantly are "Recognizing Your Opponent's Resources", which has 154 such examples. Also, "Chess Lessons" and "Maneuvering: The Art of Piece Play". That said, all of Dvoretsky's books are quite advanced, and you need to be above 2000 OTB, preferably 2200, to really benefit. His last book, "Chess Tests", was nothing but positions.

A couple of other tough books, but not as tough as Dvoretsky, are the classic "The Best Move" by Hort and Jansa, and "Test Your Chess Skills" by Sarhan Guliev and Logman Guliev. Again, both are a bit advanced, but still OK for a wider range of players.

My recommendation for most players are two outstanding series of books. The Yusupov series "Build up/Boost/Chess Evolution". There are 10 books in the series, and in each one, there is a lesson, and then a series of 12 test exercises for each lesson with just who is to move. The first four books are not simple, but they are accessible to players of a very wide range of OTB ratings. They get harder after that. This series is like having your own former top-10 GM as your teacher.

The other is the Jacob Aagaard series "Grandmaster preparation". There are 6 in this series, and there are many problems within each book. One of these books is even called "Grandmaster Preparation - Calculation".

Start with the first four Yusupov books, and go from there, is my recommendation.

P.S. The Yusupov books cover everything, from opening to tactics, to endgames, to positional play, as you specifically asked about.

P.P.S. NoseKnowsAll mentioned Silman below, and Silman posts a lot of articles he writes on chess.com. While not all are position-related, he does a lot about pawn structures, and other positions. You can find them here (click "More" at the bottom to see more of his articles to find the ones you want).