The EVGA Supernova G2 is listed as an A-tier PSU according to the tierlist, so technically the model should not be an issue. However, it's always possible to grab a faulty one for some reason. Do you have another PSU you could use for testing reasons? What is your motherboard, manufacturer and exact model (eg MSI Pro Z690-A)? You can get that reading from tools like HWInfo, for example, or your Windows installation. HWIfo can give you loads of helpful system information, too, like temperatures of your CPU and GPU. Your CPU and exact model of your GPU would be helpful, too, though I doubt that they are overwhelming your PSU since it's a 3060 and they shouldn't draw that much power. It honestly sounds like you are unlucky and got a faulty PSU. Or the electric system in your house is old and badly implemented... but I would test the PSU first before investing money to check the electric system in your home.
Edit: Something else you can try, since you say that light gaming loads don't case the issue, is to underclock or undervolt your GPU. See if that helps.