GrapheneOS kills support when Google kills security updates, I believe. Source: my Pixel 4a came out in 2020, and Graphene already strongly recommends against using it and dropped updates entirely a few months ago.
Lineage and Pixel Experience ROMs are better at long-term support. But any custom ROM on older non-officially-supported phones is vulnerable to firmware exploits, since those fixes are typically distributed as binaries by the hardware manufacturer (Qualcomm etc). So I understand why Graphene drops support so quick, since they want all Graphene users to benefit from strong security practices.
GrapheneOS kills support when Google kills security updates, I believe. Source: my Pixel 4a came out in 2020, and Graphene already strongly recommends against using it and dropped updates entirely a few months ago.
Lineage and Pixel Experience ROMs are better at long-term support. But any custom ROM on older non-officially-supported phones is vulnerable to firmware exploits, since those fixes are typically distributed as binaries by the hardware manufacturer (Qualcomm etc). So I understand why Graphene drops support so quick, since they want all Graphene users to benefit from strong security practices.