To automate the submission of opportunities into the "Secure Commitment" stage and eliminate manual submission for approval, the best feature to use is:
Record-Triggered flow optimized for Actions and Related Records (D). This type of flow allows for complex automation that can include submitting records for approval based on specific criteria being met, such as reaching a particular stage in the opportunity lifecycle. It's particularly suitable for handling related record updates and other actions like submissions for approval, which are integral when an opportunity reaches a certain stage.
Record-Triggered Flow optimized for Fast Field Updates (A) is focused primarily on quick updates to fields and may not handle the complexity of submission for approval processes adequately. Custom button and screen flow (B) could be used to manually trigger processes but does not automate the submission. Platform Event-Triggered flow (C) is typically used for integrations and reacting to system-wide events, not for standard record lifecycle management.
Reference for using Flows in Salesforce, particularly for automating business processes like approval submissions:
Record-Triggered Flows: https://help.salesforce.com/articleView?id=sf.flow_considerations_trigger_record.htm&type=5