Hi @塩崎 朋子 ,
Welcome to our forum!
Unfortunately, I didn't find any official documentation on how to clean up the New Outlook cache.
For the Cache you mentioned, do you mean the data file of the account configured in Outlook desktop client? If so, the "New" Outlook app data is stored on your Windows drive in the user's AppData folder.
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.