Big Sur - Time Machine structure

I'm running Big Sur and I noticed three things about Time Machine:

1. if I format a drive as HFS+ and then I choose it for Time Machine, it gets automatically converted to APFS without asking;
2. once a backup is completed, if I open it in Finder I can only see the data volume, as it skipped the system one;
3. local snapshots seem to be available (I can see them via tmutil) but I cannot access them in Time Machine UI.

I would need to know if these things are "normal", please.

All three are normal for TM volumes created in Big Sur.

Explanations for 2 & 3: you won't see the system volume in the Finder, but it will be available if you need to boot from the TM volume. The only reason for doing that would be to repair or restore the source.

Local Snapshots are stored on the source and are not designed to be accessed from within the TM interface.