I think the jannu alter rerun was the oldest of those? which would mean you started at the beginning of last year?
That would mean you missed
Christmas 1 (santa alter), Christmas 2 (santa lily), GUDA-GUDA 1 (nobbu), summer 1 (summer scath), prison tower (dantes/tCoMC), moon festival (orion), Halloween 1 and 2 (guess), and rashomon and onigashima (the RAITA crew)
Everything else doesn’t really have a plot (nerofest, valentine’s 1 and rerun)
Prison tower and rashomon/onigashima have actual significance, with prison tower relating to the actual main plot of the game.
Christmas 2 introduces santa alter lily. GUDA if you like GUDA.
Summer 1 and Halloween 2 are nice and even funny character spotlights. Summer 1 might be hard to understand given that every choice has three cutscene. Also part 2 is way worse than 1.
Christmas 1 is nice but is old and short and mostly hangs on whether or not you like seiba alter.
The events of Halloween 1 and moon festival are exactly what you’d expect. Liz invites you to the castle and you fight people, and Orion shows up and you think he’s Artemis for like a 5 minute conversation.
In decreasing order of recommendation.
Only those first two were actually canon to anything, honestly the trial quest stories are more canon than the rest.