Monthly Time Machine backup

There are third-party apps that allow you to change the Time Machine schedule, such as TimeMachineEditor, TimeMachineScheduler, etc. Whether they still work in Monterey I can't say since I'd rather lose only an hour's worth of work rather than a month's worth. 😎

dialabrain makes a good point. that said, in my application, a once a week backup is adequate. but, with TM, the only option is "auto backup" in which backups are constantly being made. or you need to initiate them manually. (in your case, monthly). sorry, there is no middle ground. and I cannot comment on those "scheduling" apps either. if my data was critical, I wouldn't want to trust them to 3rd party apps. frankly, in that case I would use auto backups