Hi @Gael JEHANIN
Do you mean to filter out rejected emails for meetings?
If a meeting request is declined, the meeting is not saved to your calendar and the meeting request message is moved to the Deleted Items folder.
There is no way to show a declined meeting on your calendar in Classic Outlook. You can only show accepted or tentative meetings on your calendar. It is recommended that you set rules or categories to distinguish between them.
However, you can enable it in Outlook on the web or in the new Outlook for Windows by manually checking "Show declined events in your calendar..." in Settings > Calendar > Events and invitations > Save declined events. More information, see: https://techcommunity.microsoft.com/t5/outlook-blog/show-declined-events-on-the-calendar/ba-p/3958648.

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.