A weak urine stream can occur with prostate enlargement, but it can also have other causes. The symptom is worth discussing with a clinician, especially if it is persistent or worsening.
What NIDDK says
NIDDK lists weak stream, trouble starting or keeping a stream, incomplete emptying, and dribbling among urinary symptoms that warrant medical attention.
Why “flow support” marketing can be misleading
A supplement advertisement may use language about “flow” or “prostate support,” but a marketing phrase cannot establish the cause of a weak stream and should not delay evaluation.