Big Sur TimeMachine; use APFS or APFS Case sensitive? also, bundle file extension

I backup my MacBook Air to a disk on my Mini. After installing Big Sur on the laptop I created a new APFS volume on the Mini to store the laptop's TimeMachine backups. I had two surprises:

1. TimeMachine on the laptop created an encrypted APFS Case-sensitive file system. I have no case sensitive filesystems on my laptop. Why did it choose case sensitive? I have heard of "issues" with case sensitive filesystems. Is there a way to force or trick TimeMachine into using just plain ole encrypted APFS?
2. The filesystem bundle that holds the backups is named `hostname`.sparsebundle. This seems to a throwback to earlier versions of macOS. Catalina uses the file extension "backupbundle", which seemed to be a sparsebundle plus some metadata.

But, the real question is--- after I upgrade the Mini, I'll want to create new a local APFS volume for TimeMachine. The filesystem won't get automatically generated, so should I make them encrypted APFS, or encrypted APFS Case-sensitive? Again, I have no case sensitive filesystems on the Mini. Any reason why encrypted APFS wouldn't work?