the operating system has started blocking the recognition of my non-MAC monitor

Hi patjenkins1,

Thanks for letting us know, we're glad you were able to get the external monitor working with your MacBook Air again.

Please feel free to reach out again to Apple Support Communities if you need any further help.

Best wishes.

Hey there patjenkins1,

Thanks for reaching out to the Apple Support Communities. For the best steps that can help with troubleshooting issues with your external display not being detected as expected, check out this link here: If your external display isn't detected or appears blurry when connected to your Mac - Apple Support

Before you begin

Make sure that your Mac is running the latest version of macOS.

If your display is blank or not detected

Try these steps if you don't see an image on your display.

Check your cable or adapter

Disconnect the cable from your external display from your Mac, then reconnect it. If the cable from your external display doesn't connect to the ports on your Mac, you can use a USB-C or Thunderbolt adapter. If you're using a USB-C or Thunderbolt adapter to connect a display, the adapter must be compliant with DisplayPort Alt Mode or Thunderbolt / USB 4.

Check how many displays you can connect

If you're connecting multiple displays to your Mac, use the Tech Specs page to find out how many external displays your Mac supports.

1. Choose Apple menu  > About This Mac, double-click your serial number, then press Command-C to copy it.

2. Go to the Tech Specs page, click the Search Tech Specs bar, press Command-V to enter your computer's serial number, then click Search.

3. Click the specs page for your Mac. The number of displays your Mac supports appears under Video Support or Graphics.

If still having issues after going through the steps above, we'd also recommend testing the issue in safe mode. This can help to determine if the issue may be caused by some software that has loaded when starting your MacBook up.

For steps on how to boot into safe mode, and what to do if the issue does or doesn't occur in safe mode, check out this link here: How to use safe mode on your Mac - Apple Support

Keep us updated on the results.

Take care!