In Discovery, a lot has gone on in 35 years. We've been through a few wars, revolutions and all that. It's unlikely that factions would leave any significant events without a celebration or great mourning.
So, what events would you consider significant enough to not just mention them in your RP, but to have entire events dedicated to them? And on an annual basis.
Discovery is a server of dreams. And I'm a big dreamer.
Personally I've mentioned the Maltese civil war in mine several times, very notable event inRP (and out of it). At least the one I was part of, which results in great mourning...or it should, anyway. At least for those that were present at the time. Just hazy on details unfortunately, though there is a small write-up in the old Contari Lance faction thread.
As for annual events that can just happen in people's lives, no idea if FL lore even mentions it but can probably assume that some things still occur like a time of giving (Christmas especially, which is also tied to religion), and I presume education still exists in civilised places like house space planets so summer holidays for kids or something. Guess you'd not mention the latter in your RP unless your character is a parent though.
Drawing blanks for ideas for actual events though, if you mean getting people together in the server for it. Examples off the top of my head would be the Corsair takeover of FP9, Bretonia stopping the Gauls from invading and again, Maltese civil war. Can even use vanilla FL events like the Order-Nomad stuff maybe. Not sure how you'd make events out of these though, I'm not creative enough for that on a practical level.