This maybe something simple that some people may already know but, with 2.8+ they did away with the layers system and now have collections.
I used to hit a common problem (common for me) where I would press 1 to change into vertex mode and objects would disappear. Sometimes I didn’t think I had hit the correct key (1, 2 ,3) and so would hit button again. For some reason objects would disappear.
For a long time I though it was a bug but now realize I was turning OFF all other collections except for Collection 1(or 2 or 3).
In object mode, pressing the corresponding number will display JUST that collection.
1 = Collection
2 = Collection 2
3 = Collection 3 etc
If you have renamed them, it will correspond to the order they are in. If you want to display just 2 or 3 Collections. You press SHIFT+# to add another collection and they will be displayed.
When you get up to Double Digits you press ALT+# to view that collection.
Thought it was super helpful hence the post here.