Yesterday I went crazy about missing past events too. But it was not with Odoo but Pokemon go. I joined some events and completed all the tasks and had opportunities to catch legendary pokemons. I caught half of them and saving the rest thinking that if it's mine,it'd be mine all the time and I can get it anytime. But the event is now gone with all the opportunity to encounter legendary pokes. Now I have to raid the gym everyday to farm the legendary.

With Odoo, I just check the version 18 and see that the event frontend page has filter which can show All Events (the last item on the filter list).