In the Windows version, there appears no way to create an every 3 week reminder - only weekly, bi-weekly, etc. Apparently this is possible in the Mac version.
https://community.quicken.com/discussion/7876632/scheduled-transaction-frequency-every-3-weeks-edited-clarity
Clicking the triangle does not help this in the Windows version.
As a long time Quicken user, Intuit seems to be fixing only superficial issues, and not addressing deeper structural ones.
C'mon guys. This should not be a difficult task.