A very simple script that highlights objects with ProximityPrompts inside them.

ProximityPromptHighlight.lua

--by @mvyasu
--June 2 2022

local ProximityPromptService = game:GetService("ProximityPromptService")
local Players = game:GetService("Players")

local highlightLookupDictionary = {}

ProximityPromptService.PromptShown:Connect(function(promptInstance)
	if not highlightLookupDictionary[promptInstance] then
		local highlightAdornee = promptInstance:FindFirstAncestorWhichIsA("BasePart") or promptInstance:FindFirstAncestorOfClass("Model")

		local newHighlight = Instance.new("Highlight")
		newHighlight.DepthMode = Enum.HighlightDepthMode.Occluded
		newHighlight.FillColor = Color3.fromRGB(230, 230, 230)
		newHighlight.FillTransparency = 0.75
		newHighlight.Adornee = highlightAdornee
		newHighlight.Parent = Players.LocalPlayer:WaitForChild("PlayerGui")

		highlightLookupDictionary[promptInstance] = newHighlight
	end
end)

ProximityPromptService.PromptHidden:Connect(function(promptInstance)
	local proximityPromptHighlight = highlightLookupDictionary[promptInstance]
	if proximityPromptHighlight then
		highlightLookupDictionary[promptInstance] = nil
		proximityPromptHighlight:Destroy()
	end
end)

There's an alternative way of doing this that's more simple. There was a reason why I didn't use this way in the video, but that reason is no longer relevant:

--by @mvyasu
--January 22 2023

local ProximityPromptService = game:GetService("ProximityPromptService")
local Players = game:GetService("Players")

ProximityPromptService.PromptShown:Connect(function(proximityPrompt)
	local highlightAdornee = proximityPrompt:FindFirstAncestorWhichIsA("PVInstance")

	local newHighlight = Instance.new("Highlight")
	newHighlight.DepthMode = Enum.HighlightDepthMode.Occluded
	newHighlight.FillColor = Color3.fromRGB(230, 230, 230)
	newHighlight.FillTransparency = 0.75
	newHighlight.Adornee = highlightAdornee
	newHighlight.Parent = Players.LocalPlayer:WaitForChild("PlayerGui")

	proximityPrompt.PromptHidden:Once(function()
		newHighlight:Destroy()
	end)
end)

very helpful

Help add more commands. With the item in hand, Highlight disappeared. :) Thx

Thanks