Using Ctrl+G and the Collection panel in the Object properties to create collections, creates Unlinked collections, meaning that they haven't been linked to the Scene collection. I agree that the interface here should be improved, but it's not really a bug. Use Mkey on the viewport instead (the old key to move to layers) or the New collection button on the Outliner's header. In the meantime, you can use a second outliner and change it to Orphan data to see the unlinked collections and objects, and drag them from one outliner to the other

Deleting collections from the properties of an Object could be considered a bug. The object isn't deleted, it just becomes unlinked and orphan, but nothing tells you that it will be unlinked from the Scene collection. I think by default it should remain on the scene

it's a mess i use blender since 2.4x and it was simple workflow u used groups like collections but back on topic.

i tested what u said and yes the object is acctualy in data block but problem is that i have no idea how to get it back... and i use blender since really long time... most people don't even know what we talk about... this is very confuseing and i think the workflow should be as it was, to not make another confusing change. or at least make it super simple. now is simply not working as it should i mean.. how the new people will react to this..

next thing i consider this stuff as a bug because that is generally one of the most important feature of new blender and it simply does tottaly diffrent stuff or tottaly not what u expect.

look at this, if u go by this menu it also delete object (i know it does not but... it does for 99% people)
and if u click to add to collection u can only add to collection it already exist i mean what is the point of that O_o.

next thing if u have object and u want that object to be part of few collections u can't do this by M button menu.. u have to go thru that menu in parameters windows.. that dosn't work correctly but suprisingly acctualy allows u to add one object to 2 collections.