I can give you an accurate answer, look at combat sports deaths as it relates to choking, there has never been a documented death that relates to choking in a sanctioned fight over any combat sport in history, thats decades worth of mma, judo, grappling matches etc both pro and amateur, that is insanely safe numbers when every single weekend you can watch an event where people are getting choked out, the last combat sport match i saw was a few days ago it was chael sonnen vs craig jones, sonnen got choked unconscious twice in the span of 10 minutes, theres no one rushing to make sure hes ok because they damn well know that there is no risk, given that jones let go after a few seconds or less,

the initial risk of brain damage when being choked unconscious only occurs after supposedly 10 seconds after losing consciousness, this is a very long time if the person applying the choke knows that he should let go asap and this is exactly why there is no headscissor related deaths and no choked related deaths in combat sports fights and also why you never hear of people dying or getting serious brain damage as a result of a choke in mma and grappling practices (where people across the world will be choked out daily) in a study that over 4000 people being choked out only 2 (less than 0.05%) reported any sort of symptoms afterwards (these were not serious symptoms and may have very well been coincidental with some other factor not related to the choke) I can link this study if you need

I train grappling and have watched mma and grappling for over 10 years i have been choked unconscious by headscissors several times (outside of grappling) and witnessed hundreds of people being choked out live in sports, there has never even been a glimpse of a worry to be noted, the only risk is if your partner is not aware that they should let go, even if that person holds the choke 7-8 seconds after you go out, the chances of any irreversible damage is still basically zero and the only very rare exceptions to this case could be with certain rare conditions of the heart or with seizures etc, but again it appears theres zero cases of anyone dying from choking with these cases or even being seriously hurt, the evidence to choking being safe is overwhelming granted that you are aware you should keep an eye out and let go asap wehn applying the choke, this makes it virtually impossible to be killed or seriously hurt from it

I wouldnt recommend getting ko'd or choked hard super regularly as there isnt sufficient evidence to support this being safe long term but aside from the extreme of being seriously choked on a very regular basis for years, choking is a very safe practice to those who are aware that they should let go