My workflow is not the best in beauty but it works.
The workflow accepts a start variable "first day of month".
First it will get the friendly name of that date. It will not calculate an offset to get the day of the second tuesday of the month.
If start workflow day is tuesday: add 7 days
if start workflow day is wednesday: add 8 days
and so on.
After adding these days it creates the first appointment.
From there it again adds 3 days to patching tuesday to have the friday after this tuesday. It does the same with the monday (+6 days from patching tuesday) and the next tuesday (+7 days from patching tuesday). After each addition it creates the appointments:
Resulting in the desired calendar (sorry for being denglish):
Next step would be to change the base date to the current date instead of a workflow variable and have the workflow being started on the first day of a month.