Lineage is kinda bad privacy and security wise, from the little I know its not fully degoogled
My understanding is kinda the opposite:
GrapheneOS ships with a sandboxed, FOSS Google Play Services which can optionally do a bunch of Google things (use their APIs, login to Google etc.) plus they have some hosted services that can substitute Google services (like geolocation).
LineageOS basically doesn’t ship with any Google Play style API/frameworks at all. It’s a pure AOSP experience. Any apps on F-Droid work but third party apps (like ones found on Google Play) are hit and miss. If you can just use F-Droid for all of your apps then LineageOS is probably a much more private and secure offering.
LineageOS for microG is an unofficial fork of LineageOS which includes a FOSS Google Play Services compatibility layer, a bit like GrapheneOS. As far as I know it doesn’t have the same level of sandboxing as Sandboxed Google Play on GrapheneOS.
Both GrapheneOS and LineageOS publish monthly updates with upstream security patches for all supported devices.
Both GrapheneOS use network-provided DNS by default.
Apparently both GrapheneOS and LineageOS connect to connectivitytest.gstatic.com via http as a Captive Portal test by default,althoughh this was as of 2019-2020 and both might have changed since then.