Why are some IDs grayed out or struck through?

Inactive IDs are grayed out

If a Threema ID doesn’t connect to the server for more than three months, the ID is considered inactive and will be grayed out. If the inactive ID connects to the server again, it will (after up to 24 hours) no longer be grayed out. In Settings > Appearance, there’s a setting to hide inactive IDs.

Revoked IDs are struck through

A Threema ID that has been permanently deleted is struck through and considered invalid.