From what I understand it's a little bit tricky (I also haven't read Jojolion yet so maybe it's expanded upon there).
From what I understand, still living characters from Parts 1 through 6 (such as Giorno, Josuke and I think even Joseph since he was never confirmed dead) still exist in the new timeline as their regular selves, but deceased characters were brought back reincarnated.
I thought SBR followed that same logic and was part of the same timeline as the post-Stone Ocean timeline but I could be wrong.
SBR and JoJolion take place in a complete brand new universe and that universe is not created by Made in Heaven. Its not part of Jojo 1-6 timeline.