Generally this isn't an issue for home users. Pretty much every home router defaults to denying incoming connections but allowing outgoing ones, for both IPv4 and IPv6.

In both cases you can of course configure the router to allow incoming connections on certain ports and (for IPv6) IP addresses (unless you're behind CGNAT), but it's almost never the default.

For IPv4 this happens to be a necessity of NAT: without additional configuration, the router simply doesn't know which device is being addressed because they all use the router's IPv4, so it can't forward it. For IPv6 this is a good and extremely common default firewall configuration, especially for routers intended for connecting private networks to the Internet.

The only real difference is that for outgoing IPv4 connections they typically all come from the same IPv4 (as seen from outside the local network) while for outgoing IPv6 you can potentially distinguish^1^ between different devices.

^1^: Not reliably, mind you: a device can have multiple IPv6 addresses, and many default to changing the one they use for outgoing connections every so often. Theoretically they could even re-use one that was previously used by another device, but that's vanishingly unlikely unless specifically configured to do so.