I hope this can help more people, Stay safe:
Steps (Windows Firewall)
Open Windows Security → Firewall & network protection → Advanced settings
Click Outbound Rules (left side)
Click New Rule… (right side)
Select Program → Next
Choose This program path and browse to:
...\NIKKE\Launcher\intl_service\tbs_browser.exe
(or NIKKE_HMT depending on your version)
Select Block the connection → Next
Leave Domain, Private, and Public checked → Next
Name it something like Block Nikke tbs_browser → Finish
And do that, for other launcher that has announcements on the client,
Stay safe!