I think some people get it instinctively - I do although I am let down by being vv messy and disorganised. So I can make it look nice but then I can't maintain it, or I know what I want to do, but then I never get around to doing things like painting.
But you can also learn it, as there are principles of design.
I think the first thing to do is work out a colour scheme. This is a good overview with a starting point into everything. BTW your whole house doesn't need to be on one colour scheme, as this suggests - it's just one option.
https://www.heytherehome.com/how-to-create-a-whole-home-color-palette/
The only thing I feel like is missing from this is where to start - and I would always start with aspects of the room you can't easily change. So for example, if you have flooring in good condition you want to keep, and/or woodwork you don't want to paint - start there. If these are both changeable, then look at your furniture, e.g. do you have a lot of light wood? Or black clean lines? Or busy fabrics? Or just a piece of art/photo you absolutely love and don't want to change?
Start with the piece you can't or don't want to change and look at that - if it's wood, is it cool-toned or warm-toned, if it has a picture/pattern, is there a prominent colour or a more subtle one you can pull out? Then use that starting point to go through the steps in the article above.
Colour is useful to start with, because it can make such a significant difference and usually it's one or two things which are throwing the whole colour scheme off. If you can paint/change a rug/put a throw on a sofa/paint woodwork - then it can transform a room. So figure out what your colour scheme is, see what doesn't fit, and work out if you're going to change it or move it to another room, or if that's too much hassle, rethink the colour scheme.
Once you've got an idea of colour theory you'll probably want to look into making a room flow, which basically means thinking about the purpose of each room and making the space more focused on those things and that you can move easily between any different areas of the room and that the spaces are a bit separate.
The CRAP theory is good too. If a space looks too empty or cold, add more CRAP (Curtains, Rugs, Art and Plants).
And then you look into balance and negative space. If you keep adding too much it will look cluttered - it needs some empty space. Balancing is about spreading things out so that they look good - it's not about being symmetrical.
TBH, you can't go too far wrong with wandering around IKEA, snapping pictures of any of the fake rooms you like and then seeing if they could work for your space - if you look at the fake rooms, they often have a little plan at the edge telling you the dimensions and area. The genius part being that of course you can then buy that rug, that shelf, that set of matching tasteful boxes to hide all your junk etc. And if just starting out, try taking pics in ikea, then coming home and looking at what's different and what you can recreate with what you already have.
I find Pinterest good too. If you make an account on there then search "living room" or "bohemian living room" or "scandi decor" or "modern futuristic bedroom" or anything that appeals to you at all, it will show you loads of ideas and you can start to collate (pin) anything you like to a board called "Living room inspiration" or whatever you want.
Sometimes it's hard to explain what you want in words but the more you start to put ideas on there, the more it will get to learn what you like. I also find I can get "closer to" an idea e.g. I was trying to find a look with a kitchen where the bottom cupboards were black and the top cupboards were blue, so I kept pinning lots of different black kitchens, blue kitchens, and two-tone black and white kitchens and eventually the algorithm magically pulled these together and I did find a black and blue one to show DH the idea I had in my head.
Decluttering helps a lot too - this comes fairly naturally IME with the "defining a purpose of a room" step - but is useful to do alongside the whole process of learning design in general.