

If you’re curious about the mechanics behind ELO and ELO confidence distributions after X matches, chess ELO is actually a well studied way to learn about the algorithm used by almost all SBMM. After a shockingly small number of matches, your ELO is going to end up being in the right neighborhood for you have +/- 50% WR.
I pulled that number out of my bootyhole because I knew it was a safe bet for a stable ELO.
US Chess Federation uses 25 games as your provisional ELO stage, many video games will use 10 matches. Assuming a large enough variety of ELO in the player base, you can be confident your ELO is mostly accurate after a shockingly small number of matches.