Is it possible to ride with open windows in First Class AC cabins/coupes in Indian railways?

NO

Am I correct that lower train classes may have protective metal bars on windows that limit views; so, it is better to take First AC with closed windows if one of purposes of the railway trip to see surroundings too?

2ac and 3ac also are closed....same windows, but much cheaper. Some view glass in front as an obstruction.. In lower classes, 2-3 bars are not a problem and no dirty glass.... You can always open a door and sit with the door open.

In general, you are correct, but dirty windows are the norm

You can reserve your seats on a sleeper class , make sure you opt for Lower Berth so that you get a seat near the window. In sleeper class, you can slide up or down the window and get fresh air and good view through the metal bars. If you are getting the window seat and sitting near the window, it doesnt practically limits any view unless until you are taking pictures using camera from behind the bars.

If you are lucky enough to get a window seat in a Sleeper compartment near the "emergency exit" you can probably slide up the metal bar too and it offers unobstructed view through the window.

On any AC classes, the glasses cannot be opened due to the very reason that its AC compartment. Since the glass itself would offer obstruction, there arent any additional metal bars.

So if your purpose is to see the surroundings, no matter which class you choose, Sleeper, 3AC, 2AC or 1AC make sure you are booking for Lower Berth. Only the lower berth number matches with the window seat. Well it might not be a problem in 1AC I guess.

Disagree 100%..NEVER take the bottom birth..

bottom birth.

That sounds a bit creepy when misspelled --- BERTH.

Lol..

OP .. If you take the bottom bErth, you share it with everyone...

Technically, the new rule is that you have to leave it in "sitting position" until 9pm. It's not at all enforced. And laying down and making it difficult for all your new "friends" to sit there works well.