How to confirm that nftables is enabled & in use?

Of course.

sudo nft list ruleset
sudo iptables -L

It is totally normal. Not all systemd services stay resident. That just isn’t how it works.

That isn’t confusing either, you have both installed. My advice continues to be to install iptables-nft.

As a side note, please stop linking short pastes to external websites. Instead use code blocks and put the output straight in the forum.