Much of the same rationale and questions about an after-life can be applied to the idea of ghosts, but unlike an after-life, ghosts are supposed to be in our realm.
No-one really sees ghosts. Ghosts cannot and do not exist. Some people think they see ghosts because they are susceptible to suggestion, their beliefs and the things their own minds generate.
I don’t believe Ghosts exist because there has never been any credible reproducible evidence to suggest otherwise. Anecdotal stories aren’t adequate. Photographic “evidence” is often explained by, environmental or psychological reasons and poor interpretations of photos and footage of vague visual things or even fakery.
Supposed ghostly encounters are all created by the imagination and fuelled by superstition. Just because something might have seemed vividly real, it doesn’t mean that it was. The human mind is capable of convincing us of all kinds of things that aren’t possible. We all mis-remember things on a daily basis. Our whole reality is a (close to reality) construct created by our brains. Unless you have corroborative evidence to prove what you think you saw, you shouldn’t necessarily believe it.
If ghosts existed, there would be a whole functioning and legitimate division of science working on such things, with quantifiable and reproducible results. Instead, you find small pockets of paranormal investigators that propagate and deal in unsubstantiated rubbish without a shred of valid evidence.

I have a few questions about ghosts, that by now I would have expected to have been categorically and empirically answered.

Are they physical or not? Obviously, we can’t have it both ways, and I don’t think you can realistically say that there’s a whole other branch of unknown physics that would explain an ability to have traits of physicality and no physicality, depending on what best suits the narrative. And even if this other branch existed, it would be measurable and well-studied, reproducible and exhaustively covered by now. Even if this were the explanation, why would it be something that only applies to ghosts and is not shown in anything else we observe?

If they’re physical, how can they move through things?

Are they opaque or translucent? If translucent, why?

If they’re physical, how can they appear and disappear at will?

Can they float? How is that possible? We need to harness this anti-gravity!

Can they talk? If they can, we need to harness the vast amount of information they can give us about their life, their death, everything about being a ghost etc. If they’re physical, they need energy to move and do things. Where is that coming from? Where is it stored?

Even if they’re not physical, and just made of light, where is that energy coming from? How are they storing that? We need to harness this for the good of all humanity!

If they’re just light, why can we see them as a form? What is the light being reflected or projected from? This seems like some sort of hologram technology we can’t conceive. We need to study and harness this!

If they’re not physical at all, then they definitely can’t talk or make noises, or interact with things. So there’s no poltergeists or risk or threat.

Why are ghosts so often of a historically interesting nature and found in old buildings? Why aren’t there ghosts seen in more places where they’ve died like in hospitals or sites of modern disasters? Why aren’t there ghosts EVERYWHERE? Is there some sort of lengthy period of time and certification process that distinguishes if a death of one type or another and its location passes a threshold set by some sort of ghosting council before they’re unleashed to eternally play a game of hide and seek with the living?

Do animals have ghosts? If not, why not? If there are no dogs then that’s a big fat “fuck that!” from me.

I could go on, and on with loads of reasons why ghosts are results of folklore and fallible human psychology.
You can’t just say that we don’t understand everything yet, therefore ghosts are a possibility. We understand more about how our minds fool us into believing things that aren’t real now too. Pareidolia plays a major part in ghostly experiences.

Nothing about the idea of ghosts adds up and it’s just nonsensical. People love to cling onto their beliefs though, so trying to convince people with facts, science, logic and critical thinking just won’t wash with people claiming “I know what I saw”.