Possible dumb question, but can't you FOIA basically anything in the US? Are there some restrictions in place that prevent people from requesting the trannyfesto?
I'm not sure about TN's freedom of information laws/policies but it's probably worth a shot. Florida tends to be the best when it comes to FOIA requests due to their 'Sunshine Law', they basically release fucking everything, which is why 'Florida Man' became a well-known meme. It's not necessarily that more crazy people live in Florida, or that more crazy shit happens in Florida, rather it's just due to their policy of releasing absolutely everything and that's why you hear about Florida Man doing weird shit all the time like getting arrested for fucking a pool float in public or what-not. Texas is the worst when it comes to FOIA requests, they won't release jack shit. Connecticut tightened their FOIA laws after Sandy Hook which made a lot of people suspicious but I'm inclined to believe that they just didn't want to release photographs of a pile of dead first graders in a bathroom the size of a broom closet.
Personally though I believe that they are going to keep the troonifesto under wraps at any cost until they either A) redact enough of the contents that you will not be able to learn anything about her motive or B) until the general public has largely forgotten about it and it won't make a big splash should they release it. They'll use the "well it's still an active investigation!" shit to drag their feet until the public's attention span latches on to something else. I am inclined to think they'll do the former because if they're trying this fucking hard to keep it in the dark it would either tank the LGBTQIAXYZ+ brigade's reputation among even pozzed members of the public, or alternatively it contains various smears against still living individuals. Reddit seems convinced that the latter is true, and that Hale must have been molested at the school at some point when she attended because they're still trying to redirect the [accurate] allegations of child grooming and rape amongst their own by hollering about pastors, clergy, Catholic priests, etc. It's like clockwork, bring up NAMBLA or the fact that most gay men report having been molested or raped during their adolescence, and the fact that pederasty and sleeping with underaged boys is basically accepted in the wider "gay community" and they'll instantly what-about the Catholic church. Bring up the fact that trannies are grooming children into mutilating themselves on Discord and again, "what about the Catholics though???"
We are very unlikely to see the manifesto in full, most likely excerpts if anything, but it's worth a try. Even despite them not releasing the manifesto, the attack itself was in my opinion enough to sour the average John Q. Public's opinion on the Alphabet Brigade to some extent, and probably partially responsible for some of the backlash toward 'pride month', Anheuser-Busch, etc. in recent days. That plus people are just fucking sick of 0.8% of the population dictating what other people can do or say. This type of shit plus the open, bold-faced attempts at grooming is the number one way to get people pissed off at you, you simply don't fuck with people's children, that shit is instinct and cannot be rewired out of any human being no matter how much you bend reality.