LWCから画面フローに変数を渡せません

この値を格納するコンポーネントの詳細を開くと「手動で変数を割り当て」というチェックボックスはありませんか？これを有効にしてみてください

The only thing you missed is checking the 'Manually assign variables' in the Advanced section, which would allow you to assign the output of your LWC to a variable in the flow.

https://salesforce.stackexchange.com/questions/347767/pass-a-variable-out-of-lwc-and-up-to-screen-flow-dynamically

https://issues.salesforce.com/issue/a028c00000gAyKAAA0/flow-with-lightning-component-does-not-carry-the-changed-values-into-next-screen-when-toggling-between-previous-and-next-screens