Unable to connect MacBook Air to Windows PC using LAN

What changed in the last 4 days? Software updates on Windows or Mac?

Have you looked at

System Settings -> Privacy & Security -> Local Network

Is the Microsoft RDP "Windows app" listed there, and enabled?

Boot macOS Safe Mode:

https://support.apple.com/guide/mac-help/start-up-your-mac-in-safe-mode-mh21245/mac

Safe mode should eliminate any 3rd party software interference?

Do you have Little Snitch installed? It has been known to block local connections.

rukshakhan wrote:

No not IT Support.

Well, then I think you meant to indicate that you are IT and networking support. Welcome to IT. We have cookies.

here is the ping result:

Your network functional, which means the issue is probably above the network and LAN. Something in the apps or app configuration here is blocking access, most likely.

Please download and run (free) EtreCheck, and share the results to the clipboard. Then open a new reply here, and press the Additional Text button that looks like a printed page, and paste and post the hardware and software configuration report here. From that, we can get a little more detail about what is installed and what is running here.

rukshakhan wrote:

Can I get you the details of the ping test when I get back to office. Macbook Air Laptop is in office about 30Km away.

At the command line:

ping hostname.local       # where hostname is the name of the host.
ping 203.0.113.2          # where 203.0.113.2 is replaced with the IP address of the target
traceroute 203.0.113.2    # where 203.0.113.2 is replaced

Here is a more comprehensive technical background on ping and traceroute from a major networking equipment provider: https://www.cisco.com/c/en/us/support/docs/ios-nx-os-software/ios-software-releases-121-mainline/12778-ping-traceroute.html

If you prefer the GUI, here is a free replacement (and it looks and works like the old Network Utility formerly provided by Apple):

https://www.devontechnologies.com/apps/freeware

Also: are you trying to access this stuff remotely? Because you really don’t want an openly-accessible VNC / RDP / ARD port, and because this requires configuring the intervening firewalls.

Also your second question, not sure how to get the settings on Macbook.

Are you IT support, or do you want to be IT, or do you have IT support available? I ask, because we’re heading into network IT territory.

Please describe the network in a little more detail and particularly including mention of any intervening ISP links or intervening gateway / firewall boxes, and any use of VLANs.

Please describe the outcome of tests you have run including ping and traceroute.

Which remote desktop app?

You said you were using the “Windows App”, not the older Remote Desktop app.

Notice my screenshot says “Windows App” and yours does not.

Your definition of “straightforward” and mine will differ.

What are the results of ping and traceroute?

And if any clients are set to ignore ICMP, disable and dissuade use of that setting.