Let me see if I can explain the concept of profiles better. First, as was said before, the sketch geometry you want to participate in the profile needs to exist within a single sketch. Here's an example of drawing geometry in a sketch (either with the UI or the API) and what's happening with respect to profiles.
First I draw three lines. Because there aren't any closed areas, no profiles exist.

Next, I draw a vertical line. Still, there are no closed areas so no profiles exist.

Next, I draw a second vertical line. Now there are two closed areas and as a result, two profiles now exist, as highlighted below.

An important concept to understand is that you don't have anything to do with when and how profiles are calculated. You just draw the sketch geometry and as geometry is added to the sketch, Fusion automatically calculates and creates the possible parameters. You access these automatically created profiles using the Sketch.profiles property, which returns a Profiles collection object. You can use the functionality available on the Profile object to determine which profile is the profile you want.
In most cases, when using the API, you'll draw the exact shape you want so the result is a single profile. However, there are cases where you might have multiple profiles and need to find a specific one. One approach is to use the area properties that are returned by each profile where you can get the area, perimeter, centroid, and some other area properties. Another approach is to use the ProfileLoop objects returned by a profile. This gives you geometric information about the shape of the profile and also its relationship to the original sketch geometry.
Once you have found the desired profile, you can use it to create a feature. Adding additional geometry to the sketch after a feature has been created will possibly cause the feature to compute in an undesirable way because the profile that was used as input may not exist in the same way it existed when the feature was created.
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Brian EkinsInventor and Fusion 360 API Expert
Website/Blog:
https://EkinsSolutions.com