Alternate days show notification

[MIDHUN RAJ]

I want a flow to show a variable (boolean) to be true on alternate days.
ie. day 1 var = true
day 2 var = false
day 3 var = true
day 4 var = false
......
day 31 var =....
next month
day 1 var = ....

PROBLEM:
problem is how to detect an alternate day? for that you need to compare with previous day.
example. if the day is september 30 then the next day is october 1 ...which is an alternate day
CONDITION:
The flow should work even if device is switched off for 2 days.