Such games can be organized on the basis of other gaming platforms. To do this, you need to find competitors, discuss the amount of bets in Bitcoins with them, and also find an escrow with a good reputation, which will receive contributions from all competitors and at the end of the game will give the winnings to the winner. This is certainly not the best option, but if such sites as you are looking for are missing, this option may be the solution to the problem.
Not an ideal but I thin this way could be also worth it a success. The process will take long that include the time for disucssion with the escrow and the other parties to create such agreement on using the escrow service unlike using a platform to which the site will act as the escrow and but still deductions will going to take place.
I do believe that there are platforms already that has this kind of game and this is also a trend nowadays due to pandemic all games resorted to becoming an esports where you play in a device or computer. It may be a little bit different but if you will going to get used in it the everything will be fine.