@incmiko’s answer pointed me in the right direction by looking at HKSampleQuery. However his/her code did not help me. So here is what I did to get the stroke style per lap.

private func querySwimStrokes(for sample: HKSample) {
    let sampleType = HKSampleType.quantityType(forIdentifier: .swimmingStrokeCount)!
    let sampleDate = HKQuery.predicateForSamples(withStart: sample.startDate, end: sample.endDate, options: [])
    let sortDescriptor = NSSortDescriptor(key: HKSampleSortIdentifierStartDate, ascending: false)
    
    let query = HKSampleQuery(sampleType: sampleType,
                              predicate: sampleDate,
                              limit: HKObjectQueryNoLimit,
                              sortDescriptors: [sortDescriptor]) { query, samplesOrNil, errorOrNil in
        
        samplesOrNil?.forEach({ sample in
                            
            if let quantitySample = sample as? HKQuantitySample {
                let strokes = quantitySample.quantity.doubleValue(for: HKUnit.count())
                print(strokes)
            }
            
            if let strokeStyleInt = sample.metadata?["HKSwimmingStrokeStyle"] as? Int,
               let strokeStyle = HKSwimmingStrokeStyle(rawValue: strokeStyleInt){
                print(strokeStyle)
            }
        })
    }
    
    HKHealthStore().execute(query)
}