If I create a custom Login Flow in a scratch org, and then pull using
sfdx force:source:pull, should I expect that flow to be pulled down as source? The flow created in Flow Builder is pulled, just not the "Login Flow".
The Metadata Coverage Report is the centralized location for which metadata elements are supported by functionality like Salesforce DX and the Metadata API.
LoginFlow component is not supported by source tracking, which drives
sfdx force:source:pull. It's also not supported by the Metadata API or any version of packaging. Unfortunately, you won't be able to store this component in source form other than the flow definition you've retrieved already.