you can use Flow Designer for this which runs Daily and checks if any records are there which are due 1 month from now. Iterate those and send email
check this link where I shared solution but please enhance it for your requirement
I cannot seem to get an Email Notification when a record's due date is reached
filter condition will be something like this but this is for 10 days, you can enhance it for 30 days by updating the number of days in relative operator
If my response helped please mark it correct and close the thread so that it benefits future readers.
