You will never find hard data for the entire world since most countries don't even care about that, you can start picking up country by country.
I am sure we can get some decent results with AI tools these days.What I was looking is to find clear comparison information without bunch of additional crap.
I found interesting information with BraveAI saying that all gambling in mainland China is illegal, but they are still one of the top three countries with most gamblers in the world.
United States and Japan are on top with China.
More interesting data from Brave AI:
44% of world population participated in some form of gambling in 2023!
73% of Australia adults had gambled in the past 12 months according to a study in 2023!
65% of Dutch residents participated in some form of gambling between February 2023 and February 2024!
Crypto, not Bitcoin, check the last bets tickers in casinos like bcgame or stake or anything and you will see USDT rules eveywhere
People just hold BTC these days, and mempool is mostly empty 
I dont care about USDT and other stablecoins that can be frozen and seized.
They are worse than fiat currencies, and CBDC forerunner.
- "Roughly 50% of all Bitcoin transactions are gambling-related".
This is interesting.We cant never know the exact numbers but this is a big chunk of transactions.