Implementing a Default Filter on board based on last month imported

Hi @Antoine-2 ,
 

Your request is definitely possible and to achieve it you need to leverage the Dynamic variables feature.
Let us consider the following Data Load transaction list composed of one property load month:
 

To create the Dynamic variable we would need a boolean metric flagging the last import month, in this case Nov 23.
So my formula would be: 
 

'Data Load'.'Load Month'[BY LASTNONBLANK: 'Data Load'.'Load Month'][REMOVE LASTNONBLANK: Month] = Month

The next step would be creating the Dynamic variable by accessing the Variables panel within the Settings:
 

And finally selecting this variable as the default one for the month page filter:
 

Hope this helps,
Issam