The FIDO Alliance maintains a list of what currently supports WebAuthn. If "WebAuthn API" is green, that combination of browser and OS should work fine with SimpleWebAuthn. That said, SimpleWebAuthn isn't perfect so pull requests are welcome!
Here are combinations of OS's, browsers, and authenticators that have been successfully tested with SimpleWebAuthn:
|macOS||Firefox||Yubikey Security Key NFC (USB), Yubikey 5Ci, SoloKey|
|iOS||Safari||Yubikey Security Key NFC (NFC), Yubikey 5Ci|