Three paths lead to becoming a professional pilot: Training with an airline, with a flight school or with the Armed Forces.
Austrian newspaper "Die Presse" devotes an article to this topic, highlighting Aviation Academy Austria as a representative of flight school training. This choice has to be financed by the students themselves, but it offers many advantages: All airlines can be chosen as possible employers, the training is based on a best-practice concept and the customer determines his own time budget. This allows them to pursue a professional activity in addition to their training.
Want to get more information? You can find the article here: https://www.diepresse.com/6002943/die-faszination-des-fliegens