Debugging a flow as another user
Key Takeaway
To debug a flow as another user, first turn on "Let admins debug flows as other users" in "Process Automation Settings". The setting is available only in sandbox environments.
Debugging a flow as another user lets an admin run a flow in the Flow Builder debugger as if a specific user had started it. A flow can work fine for the admin but fail for a user who has less access. Running the flow as that user shows the exact step that fails and why.
Why a flow can fail for one user
A flow that works when the admin debugs it can still fail for a user. If a user is denied access to an object or field in the org, that user is also denied it inside a flow. The running user's object and field-level security is a common reason flows break.
Sharing can block a flow even when object permissions are fine. An autolaunched flow runs in "System Context With Sharing" by default, so it can access only the records the running user can access. For example, if the org-wide default for Activities is Private, only a task's owner can see or change that task. A flow that edits tasks owned by other users then fails for the running user.