Calyx uses Google DNS & Google connectivity check (latter bypasses VPNs). Graphene built their own connectivity check (also let's you disable it altogether), and does not default to Google's DNS.

Calyx also doesn't have:

A sandboxed G Services option

Storage scopes

Attestation (Graphene built their own)

Hardening of various OS components

Hardware telemetry mitigation

Per connection MAC randomization

Not to mention security updates come in considerably faster on #grapheneos than #calyx.

Not that Calyx is bad. The above reasons might be ones to consider switching though if you're already on the fence.