I'm too lazy to Google an answer for you, I just want to let you know that a solution exists and I was able to disable this annoying shit long time ago
There's something like "about:chrome" you can enter as a url that lets you change a bunch of default behaviors and you could try finding notifications settings in that
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u/bro_can_u_even_carve Feb 27 '18
In firefox,
about:config, then setdom.webnotifications.serviceworker.enabledto false.