MacBook Pro 16" Catalina - Single or Multiple Partitions?

Your computer will appear to have a single partition. In fact it will have several which are necessary and cannot be changed. Should you choose to, you can use the built in Disk Utility program to add your own partitions. However I'd suggest that you do not. As a former Windows user, I can tell you that the most frustrating times during my switch came when I insisted on using my new Mac as if it were a Windows computer. Sure, Windows and the Mac OS have menus and windows, and mice, etc but under the cover they are very different. In the Mac world, there are few benefits in partitioning a large drive just to segregate data and more than one drawback.

Today, the only reason I'd consider partitioning my internal drive would be for the use of multiple operating systems. For example my work desktop's internal drive has two partitions: Mac OS and Windows 10.

In that regard TimeMachine is your friend. TM runs every hour backing up new and edited files since the last backup. For notebooks that aren't connected to their TM drive 24/7, snapshots are saved to the internal drive and then transferred to the TM drive once connected again. Due to the way TM works, we recommend that the TM drive have a capacity of 2-3 times larger than the source data being backed up. In this way TM will not have to delete older backups for several months. I also keep a clone backup. Should my drive die I can immediately get back to work with the clone or even use it on a completely different computer without taking time to restore.