INCORRECT...
NOTHING is fixed, the Future ALWAYS depends on what happens the Future..
We have seen many futures:
-Titans of Tomorrow (this happened in the Teen Titans Series and also in Rebirth) where Tim,Cassie,Conner,Lorena,the younger Shazam...take over the role of their mentors and become Superman,Wonder Woman,Aquawoman,Animal Man.....this is intact to some extend, because we have seen Titans of Tomorrow in Rebirth
-Batman in Betlehem (this had several interpretations) the first one was that Damian becomes Batman and Conner becomes Superman and the two argue, but honor their mentors and meet each other at this day
https://dc.fandom.com/wiki/Kon-El_(Batman_in_Bethlehem)
https://dc.fandom.com/wiki/Damian_Wa..._in_Bethlehem)
and the FUTURE keeps changing, for example neither Batman in Betlehem NOR Titans of Tomorrow included JONATHAN SAMUEL KENT until Rebirth...
AND!!!! since Rebirth Titans of Tomorrow Conner and Titans of Tomorrow Cassie and Titans of Tomorrow Bart Allen are HEROES also in the FUTURE...
Besides as far as I remind the current Tim Drake Future (Saviour) was also NOT a serial Killer, but he killed or have tried to kill Damian, because Damian became evil and he wanted to kill Batwoman,Jonathan and Damian in the present...
So its also still out of Canon..because like the recent Titans of Tomorrow in Rebirth showed that Future can change and Conner,Cassie... are Heroes in the Future and NOT Villains who terrorize the Country..