The training schemes at aircraft manufacturers are usually either 3+ year apprenticeships, or assume that the trainee arrives with a taught degree in aerospace engineering and start training from there.
I am somebody who has pursued parallel professional flying and engineering careers and qualifications, and it's worked for me - but it was never either an easy option, or a path (for me) to a full time job on an airline flight deck. For me it was about a deep passion for both strands of activity and a refusal to stop doing either.
G