APFS replaced HFS+ as format preferred by Time Machine for Destination disk since Big Sur in 2020.

[porteusconf]

Guide

"how-to-use-time-machine-and-apfs-snapshots-on-macos"

Summary

Step 2 currently (Apr 2024) says:

Step 2: format Time Machine disk as “Mac OS Extended (Journaled, Encrypted)” using “Disk Utility”
WARNING: DATA ON TIME MACHINE DISK WILL BE PERMANENTLY DELETED.

The consensus on Internet of simplest way to setup encrypted backups on new drive currently is as follows from https://apple.stackexchange.com/questions/443601/is-formatting-external-drive-with-apfs-encrypted-redundant-for-time-machine-wi
A. Format as APFS
B. Select as Time Machine Destination, and select as encrypted.
C. Time Machine will then change it from APFS to "APFS (Case-sensitive, Encrypted)"
NOTE: Because of C, there is no need to choose encrypted in step A.
So I think Step 2 should be changed to " format Time Machine disk as APFS", and add steps B and C. I will provide a screen-shot from Sonora, currently the newest MacOS version 15, below.

May also want to mention how one poster described set quotas for space used on APFS volumes that time Machine honors at https://eclecticlight.co/2021/04/15/time-machine-to-apfs-first-full-backup/#comment-60021 It requires using diskutil in the Terminal with commands like this:

diskutil ap addvolume disk6 apfs Time_Machine_BS -quota 30g -role T
diskutil ap addvolume disk6 apfs Donnees -reserve 30g