No, as an employee in Austria, your employer cannot force you to take vacation at a specific time without your agreement.
According to the Austrian Vacation Act, you are entitled to at least four weeks of vacation per year, and the timing is usually agreed upon in advance.
If your employer wants you to take vacation at a specific time and you cannot agree, you can negotiate for a mutually acceptable solution. However, your employer cannot unilaterally force you to take vacation at a specific time.
Taking breaks through vacation time is important for your health and well-being, so plan and communicate with your employer to ensure it's taken at a suitable time.