Is it possible for a Part to have an outline?

Parts can be outlined using Roblox's Selection Box object.

Create a new SelectionBox. Set its Adornee property to the part that you want to outline You can change the color, transparency and line thickness of the outline by changing the properties.

To create an outline on a part you can use a SelectionBox https://developer.roblox.com/api-reference/class/SelectionBox

Here is an example of a SelectionBox

local part = targetparthere
local box = Instance.new("SelectionBox")
box.Parent = part
box.Adornee = part

You need to use SelectionBox

The basic of SelectionBox is:

-- Put this script in part --

local part = script.Parent -- Location of part

local box = Instance.new("SelectionBox", part)
box.Adornee = part

But there are other things.

Example of 1:

-- Put this script in part --

local part = script.Parent -- Location of part

local box = Instance.new("SelectionBox", part)
box.Adornee = part

-- Change color
box.Color3 = Color3.fromRGB(255,0,0) -- Change SelectionBox Color to Red.

You can see all of Selection box in This links

1 - Selection Box Example

2 - Selection Box

Hope it helped!