Related page: https://tsed.io/getting-started/migrate-from-express.html
Related source doc: https://github.com/tsedio/tsed/edit/production/docs/getting-started/migrate-from-express.md

Looks like there's a small mistake in the initial yarn installation commands.

The second line including express and all the @tsed dependencies has the -D flag set for dev dependencies
currently it's

yarn add -D express@4 @tsed/core @tsed/di @tsed/common @tsed/schema @tsed/json-mapper @tsed/exceptions @tsed/platform-express

but should probably be

yarn add express@4 @tsed/core @tsed/di @tsed/common @tsed/schema @tsed/json-mapper @tsed/exceptions @tsed/platform-express

The npm tabs look like they are using --save and --save-dev correctly.