It does happen in Vivaldi, Firefox and all Chrome/chromium based browsers. I updated my system vie pacman gui so I think it is hardly possible that one click did something wrong. I reinstalled everything which had something to so with certificates like ca-certificates, python-certifi, etc.
But the hint with the router might be good. Even though I just updated it last week.
If I check the certifciates in the browsers under settings there are none... in dev tools it says certificates Missing.