He can force you to take the remaining days of vacation AFTER you finished being sick.

If the contract ends and you are still sick and have not taken your vacation as you had no possibility he has to pay for it.

Remember that you have to sign up as a jobseeker @ Bundesagentur für Arbeit within 3 days

Have you received a dismissal under a 'Freistellung'/ 'gardening leave' with immediate effect? Your notice for the dismissal should state this.

If they dismissed you, then they still need to observe a notice period (only very few exemption from this rule)

Depending on your contract and how long you were employed with them this may be 4 weeks, 3 months or even longer.

Because they dismissed you, they are not asking you back into work and may have put you on gardening leave (paid leave until the notice period they need to give you ends).

Under this, they are allowed to do so with calculating in/ deducting your vacation days. If your sick note covers the whole of the notice period they are supposed to give you then they will have to pay out the remaining vacation days.

In a side note, if you take your vacations and get sick during that time you can get a sick note and those days will count as being sick and not vacation time.

Then you can talk with your employer regarding those vacation days again.

Remember the fact that if you have are protected in so many ways in Germany regarding work the laws here are very strict and clear leaving very little room for interpretation.