The volume and siren on my flood light pro is very low. I rest it a bunch of times,and nothing changed. And went in my app and turned it all the way up also.
Ring considers that if you can hear the siren from about 3-5 m away then it is loud enough.
I have older, non-pro floodlight cams. The siren is loud enough to startle someone. The volume when speaking through the speakers is decently loud. It doesn’t have any volume settings in the app though.
How long have you had the pro? Could be defective. Have you tried calling Support? Or you could try exchanging from whereever you bought them.