All browser (including chome and firefox, as far as I know) will soon stop working on Windows 7 or be unable to update. It is not necessarily the fault of brave or windows but the ‘universe’ and that is why you will likely not get new updates.
Chrome
Vivaldi
Firefox (until 2023)
Edge (Until Jan 2023)
You guys are on security vulnerable old OS. To use all these browsers you will need to move to Windows 10 (or gentoo, linux). The only browser which might work on windows 7 is Palemoon.
Edit 1:-
Now if you still wish to use outdated brave on Windows 7 or 8.1 (outdated) you will need to make some changes in files to stop this notifications.
They can be done via this way https://stackoverflow.com/questions/27962454/disable-chrome-is-out-of-date-notification or other such ways.
Edit 2:-
This is the correct way to stop these notifications https://www.teddit.net/r/chrome/comments/z9ay1h/how_do_i_disable_the_to_get_future_google_chrome/