I’ve read an article which describes how to simulate the close ports as open in Linux by eBPF. That is, an outside port scanner, malicious actor, will get tricked to observe that some ports, or all of them, are open, whereas in reality they’ll be closed.
How could this be useful for the owner of a server? Wouldn’t it be better to pretend otherwise: open port -> closed?
What is a benign scan? Why do you need to scan a system if you are not trying to figure out what it is running - which is something only attackers or the server admins (looking for things that should not be exposed) would want to do. Any third party scanning for open ports I would consider an attack. Though it might just be an automated system looking for weaknesses - it is still an attack.
A benign scan could just be looking for an ftp server to connect to or a repeater or relay server of some sort. There are plenty of open services people make available for free and the fact that you would consider it an attack it doesn’t make it one.
At minimum you could be alerted to look for someone attempting to connect to your ftp server with a single basic anonymous authentication vs someone flooding that port with known malicious software attacks, and block the latter across your entire network and effectively ignore the former. Really it seems like you’re advertising your lack of imagination in this context than a legitimate lack of possible uses for spoofing open ports.