Debian supports the Raspberry Pi, best to avoid Raspbian.
Not knocking the Debian build, just wondering.
[1]: "This site is not an official Debian project. While the maintainer (Gunnar Wolf) is a Debian Developer, content herein provided should be considered unofficial. "
For SoCs, you can either do the installation on the device (which can be painful), or build a chroot with the needed features and flash it to hardware (e.g. sdcard or some board storage), https://raspi.debian.net/ is providing pre-built chroots for you to flash (but if you wanted, you could use https://salsa.debian.org/raspi-team/image-specs to build/customise your own). There's lots of similar projects which build a Debian chroot for a specific SoC, either with custom kernels or with a specific feature-set (e.g. freedombox: https://www.freedomboxfoundation.org/). None of these are "official" Debian projects (I think debian installer a.k.a. d-i is the only official/supported way of doing a install), but many are run by Debian Developers scratching a specific itch.
FYI, if you look at https://salsa.debian.org/raspi-team/image-specs/-/commits/ma..., there appears to be a fair few people who've made changes, and a least a few of them I recognise as being DDs, so it's not just one person (Gunnar Wolf is probably the person the name's been allocated to, and he probably wrote the docs). If it's security support you're thinking about, I'd put those images as more likely to have a fix early than Raspian (as those images are stock Debian, not rebuilds).
at least raspbian is very close to stock debian.
if trying to DIY your own router and you are willing to spend just a little bit more money, you can save a great deal of hassle with non-standard weird SOC-vendor-specific linux problems...
use an ordinary small x86-64 motherboard, put a 4-port intel 1000BaseT card in it, and run regular debian, or pfsense, or openbsd or something.