If there is no reason for mandatory assessment, the employee may be assessed for income tax if he or she so requests. The regular assessment period of four years applies. I.e. for 2019, the application for employee assessment can be submitted to the tax office until 31.12.2023. For 2022, the application for employee assessment can be submitted to the tax office until 12/31/2026.
Note
The employee is always obliged to submit an income tax return to the tax office when requested to do so by the tax office.