Is it permissible for an employee whose workplace is 20 minutes away from his home to combine and shorten the Dhuhr and Asr prayers, and is it permissible to perform this combination and shortening individually, or is congregational prayer necessary?

It is not permissible to shorten the four-rak'ah prayer except during travel that covers a distance of approximately 83 kilometers. It is also not permissible to combine two prayers except when there is a legitimate excuse for doing so, such as rain for someone praying alone. It is not valid to combine prayers with a single intention and a single salutation. It is obligatory for each prayer to be performed at its appointed time, as Allah Almighty says: "Indeed, prayer has been decreed upon the believers a book [i.e., obligation] of specified times," while ensuring congregational prayer for adult men.