You're all ignoring some really important facts of the situation, and I think there's a really dark answer for all this:
FACT: It is implicitly known that the "BF" was a groomer, this isn't being disputed at all.
FACT: It is obvious they have wignat/Atomwaffen adjacent mentality, and that the shooter (Samantha) did too.
FACT: They are probably not lying about being ESL.
FACT: The second manifesto feels forced, ESL, and strange.
FACT: Sending that over whatsapp makes absolutely no sense. Do we really believe this fuck-up took the time to take a PDF, put it on her phone, and specifically send it there? When the drive link already existed?
FACT: Most abusive couples, especially groomers/edaters, have logins/control over their spouses accounts. There is NO basis for him showing that it was on whatsapp being any form of evidence.
FACT: If he was actually a "she", and filled her with radfem ideology, then that would be a really useful grooming tool and way of getting her into wignat crap. Control mechanism.
FACT: NO STRAIGHT WHITE NATIONALIST COUPLE HAS MATCHING MADOKA (LESBIAN) PROFILE IMAGES.
The conclusion?
My conjecture is that this "boyfriend" was a literal German wignat pretending or masquerading as a woman. Not trans, but catfishing. He used radical feminist ideology mixed with Atomwaffen garbage to keep her in line. When she actually went out and shot people, he shat himself/lost his nerve. The new manifesto he posted was posted by him using her account to shift people off his trail.
In turn, if he had access to her accounts, he could easily have been the one who privated the drive link.
He knows he's absolutely fucked for what he did and he's trying to get people off him before the hammer comes down.