The idea would be automatically send an email each month on whatever frequency determined by dates not since last run. So the first and third Monday of every month for example.
I would realize such a scenario by using the Schedule - Recurrence trigger and set a recurrence interval e.g. each month. Next I would add a Send Email action. This combination makes sure that an email is send out at your specified interval/frequency.
You can specify advanced options:
More information about using this trigger can be found at: https://docs.microsoft.com/en-us/flow/run-scheduled-tasks . Does this answer your requirement?
The problem I have ran into is not every month is 4 weeks. So the flow is not on schedule if it is supposed to run on the 3rd week every month. (Every 3rd week is not the 3rd week of the month)
Being able to send an email on something like the third thursday of a month would be great.