The problem that you have encountered is known issue from Sequoia 15, see the below screenshots :

 

 

 

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Source :  https://discussions.apple.com/thread/255765230?sortBy=rank

 

 

To resolve the issue check the below source and screenshots :

 

Source:
[ALERT8723] Network connection lost after upgrading to macOS 15 with ESET macOS product v6

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Follow the below guide:

 

Option I: Remove the Network filter


1. On your macOS device, navigate to System Settings.

2. Click Network → Filters.

3. Select ESET Network and click the minus icon to remove it.
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4. Restart your macOS device and check if your network connection is functional.


 5. Once the internet connection is back to normal , uninstall the current old ESET Internet Security  then install latest version of ESET Cyber Security > click the source> then choose 'Install ESET Cyber Security  ((ECS will support the latest version of MacOS Sequoia 15 

 

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