Third: with your /24 subnet you told your system it has that many address to talk to. With the /32 you told it has none to talk to. With adding a route you gave the additional info „there is another network called … with a subnet of … wich you can talk to“ So your second solution is more or less equivalent but with extra steps. I don’t know how it’s implemented in the backend but it is different as in the second there is no network per default but you add routes to some. In contrast to there is a network and no routing is needed
It is a postfix representing the subnet „set bit“ prefix. Can we agree on this ?