It was announced at the end of the 2018 crossover that this year's annual crossover of the Arrowverse would be
Crisis on Infinite Earths
This crossover will go beyond the usual habit of featuring the main shows of the arrowverse in a mostly self-contained story that spans over a few episodes (one per show) and will features cameos from other shows like
Black Lightning, Smallville, the 90s Flash
Moreover, elements preparing for the Crisis has been disseminated in the arrowverse almost since its beginning, the main one being
Flash disappearing in Crisis announced by the 2024 journal since the season 1 of the Flash.
Not everybody is watching every show of the arrowverse and it is hard to keep track of everything that relates to the Crisis.
What shows and episodes relates to the arrowverse's Crisis on Infinite Earths?
Note: obviously, part of this (but not everything) is "Future Work".