What people normally refer to as "Polygon" is their Matic sidechain, which is not a "layer 2" system. It's its own consensus system with its own stake who can steal funds transferred to it from the main Ethereum network. To be considered a L2 system it has to not require additional economic majority-trust assumptions like that.
See also extended explanation: https://ethereum.org/en/layer-2/
(which doesn't mention systems like payment channels since those are limited to just payments)
Polygon the company has developed a rollup based on zero knowledge proofs but afaik that hasn't been deployed with real money yet.
Polygon zkEVM is still in alpha, but it is live and it has more than $100m in assets live on chain. Other rollups with close to $10B in assets, like Arbitrum, do exist though:
See also extended explanation: https://ethereum.org/en/layer-2/ (which doesn't mention systems like payment channels since those are limited to just payments)
Polygon the company has developed a rollup based on zero knowledge proofs but afaik that hasn't been deployed with real money yet.