Explanation
Record-triggered flow is a feature that allows administrators to automate actions that occur when a record is created or updated. Record-triggered flow can perform actions such as updating fields, creating records, sending emails, or invoking Apex code. Record-triggered flow can be used to update the account checkbox field 'Opportunity Created' when at least one related opportunity has been created

Explanation
Confirm the object is marked as deployed and not in development is what the administrator should do to resolve the issue. A custom object can be marked as deployed or in development depending on its readiness for use. A custom object that is marked as in development is not visible to users or available for data import or export. A custom object that is marked as deployed is visible to users and available for data import or export.
Therefore, the administrator should make sure that the new custom object is marked as deployed before using Data Loader to upload records to it

Multiple automation tools have been used and the automation is executed in a different order. This could cause some cases to route in unexpected ways, because the before save flow might override or conflict with the assignment rules or other automation tools that run after the record is saved. The administrator should review the order of execution and ensure that the flow logic is consistent with the other automation tools. References:
https://help.salesforce.com/s/articleView?id=sf.flow_concepts_trigger_order.htm&type=5
https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_triggers_order_of_execution.htm

An after-save autolaunched flow is a type of flow that runs in the background when a record is saved and performs actions based on the record data or changes. An after-save autolaunched flow does not require user input or interaction and can be triggered by a record-triggered flow element or by an Apex trigger. In this case, you can create an after-save autolaunched flow that runs when a Project record is created and creates a standard set of related Project Milestone records based on predefined values or variables. References:
https://help.salesforce.com/s/articleView?id=sf.flow_trigger_types.htm&type=5 https://help.sales