Hello Daniel Troyer,
Welcome to the Microsoft Q&A forum.
The message "Other users in your workspace may have access to modify this item. Do not use this item unless you trust all users who may have access to the workspace." has recently been added to the synapse workspace.
Currently, the only way to dismiss the banner is by clicking the cross option (X) as shown below.
We can't remove this permanently on the synapse workspace.
I recommend submitting a feature request to remove the banner permanently.
All the feedback shared in this forum is actively monitored and reviewed by respective product owners. Please do share the feedback link once it is posted so that I can up-vote it, and pass the feedback to respective product owners.
I hope this helps.
Please let me know if you have any further questions.