Hi Partner,
1.Why missing the 'Opportunity Sales Process' flow?
In my environment, only 'Opportunity Sales Process' flow, no 'Project Service - Opportunity Sales Process'.
Details of 'Opportunity Sales Process' as following screenshot shown:

In the description field there is a reference to the project service and the fact that it is the default, you can compare this with your BPF-'Project Service - Opportunity Sales Process', click name of it to check correct entity-opportunitysalesprocess.

I reasonably suspect that the two are the same thing, just with different Process name.
2.Difference between Lead to Opportunity Sales Process and Opportunity Sales Process
Lead to Opportunity Sales Process: Your sales process begins with a lead—someone who is interested in the products or services you provide.
Opportunity Sales Process: Your sales process starts directly with an opportunity.
These processes follow a common pattern of four stages. The first stage is similar in both processes but has a different starting point (entity) while the rest of the stages are common.
Regards,
Leah Ju
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