I’ve attached an image to show more clearly the concept of what I’m asking for.
What server/client versions are you on? I’m seeing “Add to collection” in all “Add to” menus that I can find:
Which submenu are you referring to?
Let’s look at this another way as I think it’ll be clearer as to what I’m trying to achieve… suppose I select an artist and so reveal the albums by that artist, I can then select a number of albums. A bar at the top of the screen shows the number of selected items and several icons centred, one of which is an ellipsis (…). When I click on the ellipsis, I want to see an option to add my selected items to a collection. Screenshot attached.
I was previously doing this another way (which, I now realise, was probably a lot more long-winded) by choosing the artist, and then searching for a common value so as to be able to add the resultant items into a collection. It is in that screen, when you click on the three vertical dots at the end of each listed item, that there is only the option to ‘Add to playlist’ and is where I was wanting to also see ‘Add to collection’.
At the end of the day, the ability to add multiple selected items into a collection is what I’m after 
Even the multi-select bar within the artist page has the “Add to collection” option for me. Not in the ellipsis dropdown though, from the “+☰” icon:
It’s only removed if I select multiple item types (e.g. both an individual track and an album), since I think collections can only contain a single type.
Hmmm.. missing for me - I first selected ‘Artist’ then did a search for ‘Download series’ and then selected 'Album. That produces what you see in the attached screen shot.
I suppose the challenge with dealing with search results is, they’re not restricted to a single library, while content of a collection is always part of the same library.
You’ll find the add-to-collections action when multi-selecting media from within a library.
