Not saying its like that everywhere, but Im not seeing IPv6 default usage on dual stack systems in my experience.
If you're on a Linux machine, check `ip -c addr show` for an address that's "scope global" and doesn't start with "f". Those are the ones you need. If you have one of those, check `getent ahosts google.com` to see if v6 is being sorted before v4 in DNS lookups, and then `wget google.com` to see if wget prints any errors connecting to the v6 address.
If you have GUA addresses and nothing is outright broken, devices and software that support v6 will prefer it over v6.
You are simply misinformed. Either your setup doesn’t actually support IPv6 (or it’s much slower than IPv4 due to something being misconfigured), or you turned it off at some point, or you’re making a mistake in how you measure it. Because IPv6 is used by default on systems that support it. You don’t have to take my word for this, you can google it or ask someone else to try it.