On the module settings page (/admin/config/system/seckit), there are options to configure Expect-CT.
These helpfully link to the Mozilla docs, which state:
Deprecated: This feature is no longer recommended. Though some browsers might still support it, it may have already been removed from the relevant web standards, may be in the process of being dropped, or may only be kept for compatibility purposes. Avoid using it, and update existing code if possible; see the compatibility table at the bottom of this page to guide your decision. Be aware that this feature may cease to work at any time.
I think these settings should be removed from the module, or at the very least a deprecation warning should be presented to the user on the settings page.
Closed: duplicate
2.0
Code
I'd agree this feature should be removed, but closing this as a duplicate of the older issue at 🐛 Deprecated Feature Used Expect-CT header Needs review