Alright, so after a bit of trial and error I found a solution and I thought I'd post it here in case anyone finds this thread later on.

1) Set up an AppleScript file in your "/Users/USERNAME/Library/Application Scripts/com.microsoft.Excel" folder and name it "openImgScript.scpt"

To do this, you need to open the Script Editor and create a script with the following code:
on openFileWithPath(myParamString)
    set fullPath to myParamString
    do shell script "open " & quoted form of fullPath
end openFileWithPath
This file opens an image if you pass the file's path to it.
Save it to /Users/USERNAME/Library/Application Scripts/com.microsoft.Excel/openImgScript.scpt
Note that "Library" is a hidden folder so it's a bit tricky to access it.

2) Once you placed the script to the proper location, now we gotta call this script from VBA using the following VBA code:
Sub openImgMac()
        
        'Declare path and mac script variables
        Dim myPath As String
        Dim myScriptResult As String
        
        'REPLACE WITH YOUR PATH
        myPath = "/Users/username/Documents/image.png"
        
        'open the img
        myScriptResult = AppleScriptTask("openImgScript.scpt", "OpenFileWithPath", myPath)
End Sub
3) This VBA calls the script and passes your img path as a parameter.