Keychain Access Webform Passwords Greyed Out
When using the Keychain Access application, only Certificates and Private Keys can be exported. It is not possible to to export Passwords or Notes using Keychain Access.

Migrating to a new Mac

If you're migrating to a new Mac, this is easy. Just connect your Apple ID and enable Keychain syncing with iCloud. Then when you log into your new Mac and connect the same Apple ID, your keychain contents will automatically download and sync across.

Exporting from the command line

If you really want to export your passwords, perhaps because your new laptop isn't a Mac or because you want to use a different password manager, there are ways to do that on the command-line. There's a method using security dump-keychain but that prompts for your password for every single item. To avoid typing your password many times, you can automate this with AppleScript. Or if you're using a version of macOS prior to Mojave, you might be able to use a third-party tool called keychaindump.