If you do a Google you can find shit loads of content on how to use iptables. For nftables there's 10000 blog posts on how to do NAT, and next to nothing on anything else. Sure there's the man page, and a webpage from the Devs. But examples and howtos? Good luck.
It's really hard to work it all out. Nftables doesn't help that googling for nft command has a high chance of nutrient film technique hydroponics or some crypto scam.
And by complexity. I have machines with multi hundred line nftables configs for ipv4 and ipv6 and bridging and vlans. All crafted by hand. All documented with comments. Hell my firewall config has more comments than some of the source code I've come across lately... It's a fight to find any information to make this function. It's 2 years of work.
If you want to do anything with any complexity then the documentation just isn't there. And it's really starting to piss me off. What's worse is I'm feeling really bitten by open source projects right now and not feeling particularly welcome for contributing anything. I spent 3 days trying to work out how to get one line deleted from a linux device driver, to fix a bug. I gave up because I couldn't work who to even talk to, let alone how to start the conversation.