A home we recently purchased has its fair share of wear and tear. These are things we noticed when we bought the house but just did not seem too concerning. Now about a year in - not sure if these opportunities have become more showing or we are just becoming more aware. The home was built in the late 30’s and has had a few additions. In the original part of the home we have a lot of lines in the ceilings and bulges in walls. None are soft or squishy so I know it is not caused by moisture issues or water intrusion. My gut says poor installation.. but is it worrisome? Structural? Normal?
Poor quality drywall joint finishing work - utterly normal.
Also utterly fixable, if you care to do better quality drywall finishing work.
I will normally live with it until I'm going to repaint a room anyway, and before repainting I'll bother to fix it first, since the need to repaint is the major reason to avoid drywall work. Just needs sufficient compound ("mud") feathered out nicely to provide the illusion (and it is an illusion, as a long enough straightedge will show) of a flat surface.
The very straight lines in the middle of the seam, especially as seen on the ceiling, could indicate that the tape is inadequately adhered to the drywall underneath. This happens when the mud is squeezed out from under the original tape (while applying the mud over the tape), or if too little mud was used.
While it won't be squishy, it will move just enough to make any repair you do fail over time. It will need additional attention if you don't want it to reappear.
Try pushing on the line in several places along the line. You can push hard - if it is rock solid, then Ecnerwal's solution and the solution in his link are the right way to go.
If it moves at all, then you will need to either inject glue or mud under it or cut out the sections and re-tape, depending on the size. Then follow Ecnerwal's solution and his link.
(The spot above the middle of the window looks to me like a repair of holes left behind when removing a curtain rod. I would expect similar patches to the right and left just outside of the picture.)
One thing I see in older houses is surfaces getting repeatedly painted over (modern paint on top of several layers of old paint, some of it 50+ years old). Most homeowners that do their own painting just slap the new paint on top of what's there. They don't do the extra work of surface prep and priming that's required to ensure that the new paint adheres well to the old paint. They end up with "bubbles", small sections of paint that are still connected to the paint around it but aren't attached to the surface at all. It can end up looking like the blob over your window or the wrinkly-looking bits on your window trim.
The lines in your drywall look perfectly normal to me. The general rule of thumb is that straight horizontal/vertical lines are okay. That's typically just a seam between two drywall panels that wasn't hidden well enough. Angled, jagged, or curving lines aren't good, that can indicate damage to the drywall itself.
It's hard to tell from your picture, but drywall that's only lightly textured will show these marks a lot more prominently. In some cases, the lines and bumps can be exaggerated by your lighting. I once eliminated a whole bunch of drywall imperfections simply by adding two more lamps to the room. With better lighting the bumps no longer cast a shadow, and they became almost impossible to see. Your photo looks like the primary light source is close to the wall on the left side of the window, which is just about the worst-case scenario for creating shadows from wall imperfections. You can hide a lot of that by moving the light closer to the center of the room or by adding another light source on the other side of the window.
I have a home from the late 30s and I have lots of similar issues. Some of the ceilings, in particular, have sagged over time such that you can see all the lathe-board (a precursor to drywall) seams, especially when sun is low in the sky. Even worse, top layer of plaster has broken free from the base layer forming large 'bubbles' in the ceiling. The only way to repair it is to pull the loose parts down and re-plaster. It might be worth getting a pro for doing the plastering.
Overall, it looks pretty normal to me for a house of that age. If I had to guess, I would wager that there is a 'popped' nail under that spot above the window frame. As the seasons change it moves and pushes out the plaster.