I firstly just gave a background on why it is happening, and users should know the disadvantages of using W7, 8.1. I wrote this first part for only those users in this thread which might not know the disadvantages.
Lets say in a hypothetical scenario, I do not provide such a disclaimer at all and some user’s brave browser get ‘hacked’ due to a JIT high level vulnerability (chromium had to patch 22 such vulnerability this year alone. Just yesterday a major chromium 0 day was repaired https://www.ghacks.net/2022/12/03/chrome-108-update-fixes-security-issue-that-is-exploited-in-the-wild/) or a memory corruption vulnerability and the device is completely taken over. Someone might blame me for not telling them about the disadvantages (in reality no one will actually blame me).
I know that 90% of users in this thread exactly know why the notification is there. Why happens with using outdated OS along with outdated browser, but still I wanted to giving a disclaimer for the rest of 10% users.
Later on, I did provide a link for a stack over flow thread which might be used to create changes which could be used to disabled such notifications.