If you are willing to use a script mod you can enable back most events with a small, 6 lines script mod. The following script enables the Day of the Dead challenge:
import server.online_tests
from event_testing.results import TestResult
def add_live_event(self):
if (self.event_id == 'fallchallenge'): return TestResult.TRUE
return TestResult.NONE
server.online_tests.IsLiveEventActive.__call__ = add_live_event
To use it, create inside your Documents\Electronic Arts\The Sims 4\Mods folder a new folder named unzippedScripts. Inside that new folder create another one named Scripts. Create a text file inside the Documents\Electronic Arts\The Sims 4\Mods\unzippedScripts\Scripts folder, paste the above content, and save it with a .py extension (you might need to enable the showing of file extensions on Explorer in order to change the extension). Don't forget to enable script mods inside the game. If you did everything right it will enable the Day of the Dead event (while disabling whichever other event might be running), though the NPC that will give you the event will still be Millie Bobby Brown instead of Jasmine Holiday due to a bug introduced in the 1.47.51 patch.
To undo the change, either delete the file or change its extension to something else.
'fallchallenge' can be changed to the internal name of any event in order to enable it. The events I'm aware of are:
'springchallenge': Plant Sim challenge.
'fallchallenge': Day of the Dead.
'positivechallenge': Positivity Challenge
'gardboost': the Triple Boost Week
'doublexpweekend', 'doublespmotive', 'doublerel': All the different double boosts, self-explanatory names.
You can't re-enable the Egg Hunt event this way, as it was removed from the game and added back in Seasons as a holiday, albeit one you need to add yourself. The Growfruit event was also removed, but I'm not aware of it being added back in any shape or way.