I will post here a complete collectibles guide. There are 198 collectibles in the game. 62 Letters (46 Letters in fixed locations, 16 letters random in chests), 48 Relics, 48 Blue Cats, 32 Jars and 8 golden Cats which requires the 48 blue cats to unlock the cat door for each golden cat.
Please keep in mind that the 16 letter collectibles from the categories "Tales of the Strange Brigade" and "The Legends of Seteki" are randomly located in treasure chests and are not part of this guide. This guide only shows the collectibles with a fixed location and being counted in the mission overview (182 instead of 198)
In the first spoiler is the video, in the second spoiler the timeline and in the third spoiler the timeline sorted by categoryHarbin's Dig Site
Tunnels Of Wadjet
The Towering Temple