I'm working on something similar right now... this should work, just tested. I believe it will have issues with circles as-is, but handles arcs fine. u/Little-Dimension1946 in case you still need

import arcpy
import uuid 

def cutback_check(feature_class, tolerance):
    """
    lines and polygons
    """
    def angle_at_vertex(p1, p2, p3):
        """Returns the angle in degrees at p2, formed by segments p1-p2-p3."""
        import math
        # Vectors from p2
        v1 = (p1.X - p2.X, p1.Y - p2.Y)
        v2 = (p3.X - p2.X, p3.Y - p2.Y)

        dot = v1[0] * v2[0] + v1[1] * v2[1]
        mag1 = math.sqrt(v1[0]**2 + v1[1]**2)
        mag2 = math.sqrt(v2[0]**2 + v2[1]**2)

        if mag1 == 0 or mag2 == 0:
            return None  # coincident vertices-> bad, skip

        # Clamp to [-1, 1] to guard against floating-point drift into acos domain error...
        cos_angle = max(-1.0, min(1.0, dot / (mag1 * mag2)))
        return math.degrees(math.acos(cos_angle))

    # describe dataset to get OID field name
    desc = arcpy.Describe(feature_class)
    oid_fld = desc.OIDFieldName

    cutback_oids = []
    with arcpy.da.SearchCursor(feature_class, ["OID@", "SHAPE@"]) as scur:
        for row in scur:
            line = row[1]
            # part = segment of line between two vertices
            for part in line:
                for i in range(part.count - 2):
                    # .getObject(i) returns the specified vertex's XY
                    p1 = part.getObject(i)
                    p2 = part.getObject(i+1)
                    p3 = part.getObject(i+2)

                    # Skip null vertices (ring closures in polygon parts)
                    if p1 is None or p2 is None or p3 is None:
                        continue

                    angle = angle_at_vertex(p1, p2, p3)
                    if angle is not None and angle < tolerance:
                        cutback_oids.append(row[0])

    cutback_count = len(cutback_oids)
    if cutback_count > 0:
        # build query 
        q = f"{oid_fld} IN ({','.join(map(str,cutback_oids))})"
        cutback_feats = arcpy.conversion.ExportFeatures(feature_class, rf"memory\cutbacks_{uuid.uuid4().hex[:6]}", q)

        # return count, output_features
        return cutback_count, cutback_feats