DIAGNOSTIC TOOLS
Use Apple Diagnostics to test your Mac
  https://support.apple.com/en-us/HT202731   
  If you think your Mac might have a hardware issue, you can
  use Apple Diagnostics to help determine which hardware
  component might be at fault. Apple Diagnostics also suggests
  solutions and helps you contact Apple Support for
  assistance.
EtreCheckPro (free) - for power users
  https://etrecheck.com/about
  https://etrecheck.com/details
CleanMyMac (not free, but excellent)
  https://macpaw.com/cleanmymac   
  CleanMyMac is all-in-one package to awesomize your Mac. It
  cleans megatons of junk and makes your computer run faster.
  Just like it did on day one.
Malwarebytes (free)
  https://www.malwarebytes.com/mac-download/   
  Proven Malwarebytes technology crushes the growing threat
  of Mac malware, including thorough malware, spyware, and
  virus removal. Finally, cybersecurity smart enough for
  the Mac.
  
CONNECTIVITY
  Connectivity (internet) 
  WiFi Connectivity 
SCREEN SHARING
Share your screen using Messages on Mac
  https://support.apple.com/guide/messages/screen-sharing-icht11883/mac   
Share the screen of another Mac
  https://support.apple.com/guide/mac-help/share-the-screen-of-another-mac-mh14066/mac   
  One important capability available to Mac owners is the
  ability to screen share between any two Mac computers over
  the internet. With the permission of both parties the
  initiator can share remote owner's screen, sound and cursor
  function.
  
Siri "Launch Screen Sharing"
  
  
  
DFU (User Beware)
Everything You Need to Know - DFU Mode for iOS/iPadOS Devices
  https://www.ifixit.com/News/41428/everything-you-need-to-know-about-dfu-mode-for-ios-devices
  The DFU Mode in iPhones and iPads is an emergency tool
  that's not designed for most people to ever see. It's hard
  to activate, and the screen stays blank when you finally
  manage to trigger it. And yet this obscure tool is essential
  for resurrecting a dead iPhone, or rolling back an unwanted
  iOS update.
  DFU Mode is more powerful than Recovery Mode, and is
  unsupported and undocumented for us, the end user. It lets
  an iOS device connect and talk to iTunes (or its Finder
  equivalent in macOS Catalina), without loading the
  bootloader, or iOS itself. As its full name - Device Firmware
  Update Mode - suggests, the mode is used to update the actual
  firmware of the device, mostly to install a boot loader.
  DFU Mode is hard to enter, requiring convoluted sequences of
  button presses to enter. Even when you reach DFU Mode, the
  screen remains blank.
  Unlike recovery mode, which can be updated with a software
  update, DFU is burned into the hardware, and cannot be
  altered. But it's a powerful tool. Because it works at a
  lower level than Recovery Mode, DFU lets you do things not
  allowed in Recovery Mode.
     
  
  
 
    sam.wormley@icloud.com