DUPLICATE YOUR PROJECT TO CREATE A SAFE COPY. You don't want to ruin an original by accident.
TLDR at bottom
Depending on the qualities of the render, one may need two or three different viewlayers. Keep in mind when you create new view layers, render times take longer.
Start by creating a new collection and isolating the In-Front object(s) in said collection. Call this AlwaysOver(Alpha)Collection [also known as Collection 3].
For accurate lighting, you want to duplicate all light sources and place them inside the same layer as the In-Front object. In the In-Front collection, if a light source is an emission object, you want to go to Object Properties - Ray Visibility - uncheck Camera, if not done so already. This makes emission materials emit light but lets the camera pass through the emission object.
Now you want to duplicate your view layer once or twice:
One time if you don't want shadows or reflections of the In-Front object interfering with any other objects, and vise versa.
Two times if you want shadows and reflections to interfere (can create some trippy effects).
If you have two viewlayers, name them as such:
(OPTIONAL) With three viewlayers, name them as such:
You now want to create 4 total collections: Two for your AlwaysOver object(s) and two 'for' your backgrounds. Name Collection 1 "BackgroundCollection" and it should contain the entire scene except the AlwaysOver object.
Duplicate Collection 3, rename it AlwaysOver Shadows + Reflections. This is collection 2. It should contain ONLY your AlwaysOver object, no lights, so delete the lights in this collection. The AlwaysOver object in this collection needs a property change. Have unchecked the property 'Camera' in Object Properties - Ray Visibility - Camera. This makes camera rays pass through it, important later.
Collection 3, AKA AlwaysOver(Alpha)Collection [described above] should be similar to Collection 2. The property 'Camera' in Object Properties - Ray Visibility - Camera should be checked so it is visible during renders. Lights should not be deleted in this collection.
(OPTIONAL) To create Collection 4, Duplicate Collection 1, AKA BackgroundCollection. In Collection 4, which should be renamed BackgroundHoldoutCollection, you need to delete all lights, including emission lights. These emission lights will be visible in other layers. If you mess up any lights, some lights will be twice as bright or not at all. Now you want to select every single object and make it a holdout object under Object Properties - Ray Visibility - Camera.
Go to your first Viewlayer, AKA BackgroundView. Collection 1 and 2, "BackgroundCollection" and "AlwaysOver Shadows + Reflections" Should be turned on, with every other collection turned off.
Go to your second Viewlayer, AKA AlwaysOverAlphaView. Collection 3, AKA "AlwaysOver(Alpha)Collection" should be turned on, with every other collection turned off.
(OPTIONAL) Go to your final viewlayer, AKA HoldoutView. Turn on Collections AlwaysOver(Alpha)Collection (Collection 3) and BackgroundHoldoutCollection (Collection 4) with the other 2 collections being invisible/off.
1st Compositing step
Go to the auto-generated compositing workspace in Blender, or create it yourself. Check "Use Nodes" at the top.
Create a new node "File Output" And change its details to be EXR Multilayer. Now you want 4 inputs: "Background" "AlwaysOverCol" "AlwaysOverAlpha" and "Holdout" (although if you were planning on doing compositing already you may need more inputs. If so, seperate inputs based off of the viewlayer and combine them into 4 images before I describe the 2nd compositing step).
Add 3 render layer nodes: Each should have each individual viewlayer (2 if you're doing the minimum). Connect them to their corresponding inputs on the file output (EXR multilayer) node.
2nd Compositing step
Mute the nodes you just created. Highlight them and press m to do so.
Just follow what I did here, but here's some words in case the image disappears.
Create an image node. It should have 3 (OPTIONAL: 4) images when you select the EXR file. Below describes what 4 images should give you.
Connect AlwaysOverCol and Holdout to an alpha over node (in image) [Fac should be 1.0]. Holdout should be bottom image slot, AlwaysOverCol should be top image slot. Now this completed alpha over node should connect to a set alpha node (image) with AlwaysOverAlpha (From original 4 piece image node) connecting to "alpha." Apply mask should be selected, otherwise double blur will occur and the AlwaysOver object won't look exactly right. Connect the Setalpha node to another Alpha Over node (Image - Bottom) and connect Background (From original 4 piece image node) to the other Image slot. Factor of one. Connect this final Alpha over node to a file output.
Results (Cube stays at a scale of one the entire time):
If using 3 images (bare minimum), skip the first alpha over node. AlwaysOverCol (From original 4 piece image node) should connect to the Set Alpha Node in Image, with AlwaysOverAlpha connecting to Alpha. The rest is described above.
Results for 2 view layers:
render 1st viewlayer w background with AlwaysOver obj shadow, no AlwaysOver obj visiblity, with AlwaysOver obj reflections in other objects
render 2nd viewlayer just AlwaysOver Obj for alpha + alpha channel plus scene lighting (Emission objects invisible to camera rays)
(Optional) render 3rd viewlayer Holdout channel for every object except the alpha over object, including emission lights
Side note: In the BackgroundCollection you can choose to disable AlwaysOver object shadows if you want. That will change the 'look' and abstract-ness of your final piece.