Laravel 9 is now supported in release v17.2.0 which you can use now.

As mentioned in the releases, this will be the last release which supports PHP7.x as there's some backwards compatibility blockers now trying to maintain 8.1 engine functionality while being backwards compatible with PHP7.x.

v18.0 which will be coming soon, is going to be a minimum requirement of PHP8.0, this will have the latest changes to the basic shopify api.