When SSR mode is added to a TypeScript project, Quasar scaffolds TypeScript files in /src-ssr. If the project was converted to TypeScript after SSR mode was added, rename the .js files in /src-ssr to .ts and apply the required type annotations.

Check the SSR Webserver and SSR Middleware pages for examples with TypeScript.

Depending on the webserver of your choice, you may also need to additionally install @types/* packages into your /src-ssr folder.