When you say you have an event every 2 days except weekends, I suppose you're trying to say: MoWeFr (week 1), TuTh (week 2), MoWeFr (week 3)... is that right?
The basic structure of iCalendar (the one used by Rainlendar) is more complicated than you think. The standard takes for example this Recurrence Rule: RRULE:FREQ=YEARLY;INTERVAL=2;BYMONTH=1;BYDAY=SU;BYHOUR=8,9;BYMINUTE=30
This means: an event that happens at 8:30 and 9:30 every Sunday of January every 2 years.
Of course, I'm not saying that what you want is something impossible. In fact, your rule would be: RRULE:FREQ=DAILY;INTERVAL=2;BYDAY=MO,TU,WE,TH,FR. Or only with the interval and setting the exception rule as EXRULE:FREQ=WEEKLY;BYDAY=SA,SU. The problem is that there are thousands of combinations of the recurrence rule.
Maybe you have luck and Rainy add your rule.
As a workaround, I suppose you can split it in 2 events:
The first one, on Monday, Wednesday and Friday every 2 weeks;
the second one, on Tuesday and Thursday every 2 weeks, starting the next week of the above.
