Manual Time Machine Backups

I've had iMacs for longer than I care to remember. Time Machine was always "Automatic" and pretty much set and forget. In all the time I've had Macintosh computers (going back to 1984) I've only used a Time Machine backup once to get me out of a jam, and it worked perfectly. So it's a good thing.

But, I now have a new MacBook Pro, M1 running Big Sur and do not keep an external drive connected as I travel, so I thought I'd manually start Time Machine and backup once I'm back home and can connect the external drive.

Apple states Time Machine keeps:

Local snapshots as space permits.

Hourly backups for the past 24 hours.

Daily backups for the past month.

Weekly backups for all previous months.

Obviously this does not apply to doing Time Machine backups manually. But, what I have found is that in "manual", Time Machine seems to ignore all of the above and keeps EVERYTHING! I had a Samsung 500GB external SSD and within a month or so, it was full.

So, is there a manual backup strategy that someone can share as to how to do manual Time Machine backups and not fill up drives faster than Amazon can ship them?