I made one not too long ago that works under current mIRC, but I packaged it as an add-on for the Peace-and-Protection script. (Because I wanted to re-use some utility code in PnP -
https://github.com/peace-and-protection) You'll find the add-on in the PnPAddons422 repository. While it may not answer your main question 100%, anyone is free to grab whatever
code you need to make it work under standard / vanilla mIRC.
A few pictures:
N.B.:
1) It doesn't send to channel(s), only to a custom window in your mIRC;
2) It doesn't use dlls, but COM. I tested it to work under Win 10;
3) It only works with selectnodes rss/channel/item, meaning it won't work for the Atom standard. (Only RSS);
4) PnP uses
option dbu for dialogs, which presents display issues on Windows with desktop scaling > 100%;
5) PnP is over 20 years old, but still runs a dream. Some ppl may yell at you for using it though!
Hope this helps