Is Windows Server in EC2 free?

The cost of windows is included in the hourly rate. See pricing details here - https://aws.amazon.com/ec2/pricing/on-demand/.

For new account 1 year is the free tier limit and in this you get 750Hrs/month for Windows instance and 750Hrs/month for Linux EC2 instance only free tier available AMIs are free. If monthly utilization exceeds 750Hrs then you will get charged /sec or /hr basis and If you don't have free tier account i.e. account is older than 1 year you won't get any free tier and will be charged /sec or /hr basis for your resources utilization. I hope this might be helpful ...!!!

Also take a look at the cost calculator

https://calculator.aws/#/

An example for the following config in us-east-1 works out at 1,506.84 USD for 12 months

Operating system (Windows Server), Quantity (1), Pricing strategy (EC2 Instance Savings Plans 1 Year No Upfront), Storage amount (30 GB), Instance type (t3a.xlarge)

https://calculator.aws/#/estimate?id=36039b733271ecb5b7dfcd8a05df2ec2539029a5