In Salary, holiday is set to expire automatically by the end of the corresponding holiday-taking period (this means that holiday accrued in 2020, will expire on December 31, 2021).
In accordance with the Danish Holiday Act, the employer and employee can make a written agreement that unused holiday can be transferred to the following holiday year. This can be implemented on a company level by setting up an automatic transfer of holiday to the following holiday year 1/1 202x in Salary.
You can specify the number os days that can be transferred (usually 5 days) under Company -> Holiday settings:
Write the number of days and choose Save changes.