@Gustavo
It's the All Singles Best she teased in January 2020 already.
Singles from TAKE BACK till XXKK (so 92 songs altogether without mop and WBL). They probably simply pushed it back for a year and it was originally planned to be released December 6th 2020.
The description directly mentions TAKE BACK, Ai no Uta and XXKK.
Fans sre already calling it 20th anniversary best album.
Which it is.
The actual interesting thing will be how many songs are going to be on those two versions in total, if there are going to be new songs as well or maybe just a new song through video and what else they include.
EDIT:
Ok, it was December 2019 when she teased it, lol.
Gonna include it again: