I cut my teeth on an early version of The Linux Networking Howto, still available at tldp.org. That’s a little bit out of date now :-) but the basic IPv4 networking concepts are still good.
These days so much is implementation or distribution dependent. There has been so much very rapid development in this field during the internet era that the age of documentation matters significantly.
A mitigating, but also confusing, factor is that different generations of networking tools have backwards compatibility built in so that it has been possible to build firewalls on kernels running nftables using iptables utilities in userspace.
I think you could do worse than starting with the Debian wikis and then drilling down into other documentation for the specific distributions or applications you want to use.
I seem to remember that openwrt.org and shorewall.org (though that product is EOL) also have some good overarching network stuff. I think Hurricane Electric he.com may still do their free basic IPv6 certificate programme?
Wikipedia is also your friend in this, especially the references.
I’ve enjoyed onemarcfifty.com’s videos too, but that format isn’t what you are looking for, and the transcripts I have seen are not formatted.
Procmail for the old school win.