You're better off using cdk deploy --method=prepare-change-set. That's the method we use in order to review changesets before approving execution of them. The benefit of this over cdk synth is 1) as others have mentioned, AWS lookups that determine template values need to be specific to your deployment environment since some things end up hardcoded in the template, and 2) any new S3 asset versions are uploaded during deploy even if you don't execute the changeset, so everything is just ready to go for when you do execute the changeset. So you're not technically executing the generated template file, but you are adding an intermediate step for validation which is usually the goal here.

However, it is also possible to combine the two - run cdk deploy to generate templates and upload assets, and then just ignore the created changeset and manually execute the template file itself.