To really catch up on everything between Dark Nights Metal and Death Metal you need to read:
Justice League: No Justice [4 issues]
https://www.dcuniverse.com/collections/story-jl-no-justice
Justice League (2018-) [First 39 issues]
https://www.dcuniverse.com/comics/series/justice-league-2018/78245a35-4e35-4f82-bae2-763e165629e1
It’s a lot of reading, but will fill in the Perpetua gaps for you. Or you can search for summary videos on youtube 
.