Eventually I got a Nuki Opener which works with all kinds of intercoms and is way less effort. Janky builds are awesome but better for the playground than as a solution you really want to be reliable for the whole family.
P.S. The code from the article should be linked more prominently [0], for anyone who wants to tinker.
I have it configured with a delayed opening so that it's not obvious, it doesn't require an app, and by the time you reach the door, the guest is almost there.
When I'm done with it, I flip the switch. It's hard to have it more reliable than this for me.
I've been considering smarter iterations for myself, but I didn't find enough time to fix something that is working really well.
But it also supports more complicated setups like digital intercoms where it will hook on the bus and learn the various codes that are sent for different operations, or enable the voice function through the phone app.
The biggest benefit is that if your intercom is compatible, it just works. It's the convenience, not that you can't get the same with a janky solution with enough elbow grease. No need to tinker with the firmware, the batteries last forever, and even in the most basic setup you'll have a few more advanced features.