UbiKobold
I completed 2 Timed-Limited Challenges in Immortals Fenyx Rising
Forager - Gather Blue Mushrooms
Many-Armed Army - Defeat Hekatonchires
Both didn't pop up in-game upon completion - claimed Rewards
Also in AC Valhalla, completing the Time-Limited Challenge:
Valkyrie's Dirty Work - Avenge The Death of Other Players
resulted in me Leveling Up
but no in-game notification
I have no other games installed that I can test it on.