Actually that knowledge gets used often as has been around for more than 6 months, and will be around 6 months from now
And to help you, in my sig (and here) is an easy (if youre running windows x64) tool to extract the boot image from payload.bin (inside the ROM zip).
1) download payload_dumper-win64.zip and extract
2) extract payload.bin from ROM and put in payload_dumper-win64\payload_input folder
3) run payload_dumper.exe
4) monitor payload_output folder - once theres more than boot.img in there, you can kill the process if yuo liek to avoid extracting all the images
5) copy boot.img file to device
6) patch with magisk
7) move magisk_patched.img back to PC
8) flash with fastboot flash boot <magisk_patched.img>
9) reboot with fastboot reboot
Holler if you are not using windows, theres a tool for every OS...
Some ROM devs will include a boot.img file separately (like ABC ROM), some wont. But now you have the knowledge, and a tool for those