Iran general says more than 300 dead in Amini unrest

Yeah, you can either believe the eyewitness who said she was severely beaten on her way to the briefing class, or the video that clearly shows she was not severely beaten prior to her collapse

The video do not say she was not beaten, it only shows she was still able to walk and talk, anything other than that is just you making assumptions. The witness are not the only argument that says she was mishandled, the own government of Iran is the one giving contradictory stories to "explain" her death.

People with serious injuries usually don't walk as if nothing happened

They can and do, not all injuries are incapacitating before death, a brain hemorrhage for example can have only mild symptoms before suddenly being able to put in risk the life of the victim. Without an authority looking at the body (something Iran is not letting happen) you have no argument except that you believe the video says something.

She looked perfectly fine until she suddenly collapsed, as has happened to many people for the past two years.

No, as it has happened since always, because sudden death is something that happens, specially for people that have been subjected to violence recently as the accusations say in her case.

Yeah, you can either believe the eyewitness who said she was severely beaten on her way to the briefing class, or the video that clearly shows she was not severely beaten prior to her collapse. People with serious injuries usually don't walk as if nothing happened and then talk about their clothing. She looked perfectly fine until she suddenly collapsed, as has happened to many people for the past two years.

She was arrested and was apparently expected to undergo a "briefing class" and released an hour later

All this under policy custody, and under accusations of being abused while in transport. This means her death comes in the best case scenario under the responsibility of the police, and if the testimony of witness believed as a direct consequence of abuse.

It seems she had a preexisting condition, or perhaps she got an injection prior to visiting Tehran...

No evidence whatsoever for any of those things, specially no injection of any kind, much less of anything related to being in a coma for two days afterward, unless your argument is that she was poisoned by the police.

If you actually look at the video, you'll see that she was fine prior to suddenly collapsing:

No, you can see she appears fine, which is something completely different. People can have serious injuries that will not be evident in a few seconds of video that could cost them their lives. The conficting evidence released by the Iranian government and the opposite declarations of witness and family of the victim point are the reasons why the population do not trust the official position.

Are you arguing that she had a congenital or preexisting condition that was completely unrelated to the treatment she got for 3 days under police custody...

She was arrested and was apparently expected to undergo a "briefing class" and released an hour later. Unfortunately, she suddenly collapsed while waiting in the classroom, and remained in a coma for 2 days in hospital.

It seems she had a preexisting condition, or perhaps she got an injection prior to visiting Tehran...

If you actually look at the video, you'll see that she was fine prior to suddenly collapsing:

https://www.youtube.com/watch?v=Wku5TCIghDg

Why are they protesting for this?

Because she died under the responsibility of the police, custody comes with it.

 It looked very much like the many videos we can see online of certain people collapsing.

Are you arguing that she had a congenital or preexisting condition that was completely unrelated to the treatment she got for 3 days under police custody (as the people in videos)? do you have any evidence to support this?

Iran has for the first time reported that more than 300 people have died in over two months of protests sparked by the death of Mahsa Amini in police custody.

Why are they protesting for this? Iran quickly released the video, where you can see her walk into a waiting room. She looked perfectly fine as she was chatting with two other women about her clothing, and then she suddenly collapsed. It looked very much like the many videos we can see online of certain people collapsing.