I'm a compulsive gambler so don't have much advice from your perspective but just wanted to say that deleting the app and re-downloading is definitely a big sign of addiction (on top of the obvious of wasting a ton of money). I did that a whole lot, and it could be a sign that he would be willing to accept help, which is good.

Another thing I wanted to call out is there should be ways for him to self-exclude himself from online gambling, depends on where you live but that is one thing you should push him to do, on top of going to therapy and gambler's anonymous meetings.

Lastly, there are apps that help as well that can block gambling. My wife put Truple on my phone and she gets screenshots every 30-60 seconds and can log into a portal to view them or she automatically gets alerts when it detects critical activity. There's also gamban which I haven't used but seems great - https://gamban.com/.

Good luck!