Many thanks for your detailed reply. In response to these issues:
>>1 - Is it mandatory in an autonomous agent to create a flow? (In that exemple I don't use a flow)
Yes, it's necessary for there to be a flow. This would normally be created automatically when you create the trigger. If there's something wrong with that flow, that would be an explanation for the issue you're seeing. In the screenshot I posted, you'll notice the first action that runs when executed by the trigger is the 'Search Sources' action. This is missing in the video you posted, so it may well be something wrong in the flow that's the cause of this.
The flow should look like this and contain these 2 steps only.
>>2 - Do you think it can be related to the environement?
I don't think this related to the environment. I created my example above in my developer environment in the PowerUp tenant which should match the setup you have.
With regards to your observation about the agent not correctly retrieving the manager, it might be related to it struggling to lookup the record based on an SharePoint Choice field. I'll see if I can reproduce this.
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At this point, it might be worth creating a new agent from scratch to see if it works better.
I would suggest just starting off with the SharePoint and single Welcome.docx knowledge source, and seeing if the agent references Welcome.docx when triggered autonomously. If that works, I would then add in the additional knowledge source and retest. If that then works, I would then add the tool/flow to create the record in SharePoint.
Hopefully doing it step by step like this might work better.