Currently Polymarket charges no fee for trading, and no fee for deposits and withdrawals.
https://docs.polymarket.com/#api
https://legacy-docs.polymarket.com/getting-started/depositing-usdc
(*There are a $0.08 flat fee for deposits, which clearly is just there to cover the cost receiving deposits instead of a way to make profit)

When will Polymarket start charging a fee for trading or deposits or withdrawals as a way for the company to start becoming profitable?
Resolves Yes if Polymarket start charging a significant fee.
Any of the following fee would qualify for resolving yes:
1. Any fee for trading (flat or percentage)
2. A flat deposit fee larger than $1, or any percentage deposit fee > 0.5%
3. A flat withdrawal fee larger than $1, or any percentage withdrawal fee > 0.5%