I know of two methods.
You can use github workflow as described here:
You need to setup a GitHub account and push your source code to your remote repository. Then add the GitHub workflow file made by @qno to the repository. Now each time you push changes to your remote repository, if all goes well, the linux, mac, windows and arm builds can be found in the artifacts section of the actions tab on GitHub.
Another method is setting up your system so that it can build linux, windows, mac and arm locally by following the instructions on the rack-plugin-toolchain page: