Inbound/outbound trips within your country of residence

Hello, I see this topic has been debated before, but reading through the forum I don’t find a definitive answer.
So here is the question: can I use two inbound trips or two outbound trips from my country of residence, or does it have to necessarily be one inbound and one outbound?
The Interrail website/rules state that it should be one inbound and one outbound.
The Eurail app doesn’t really seem to care, as long as no more than two days are used. But I never tried.
The answers to previous similar questions on this forum all say that it “should” be ok to do two inbounds or two outbounds, but I don’t find a solid it “IS” ok to do so.
Does anyone know for sure? I don’t want to be in the position of having the app reject my travel plan when I’m about to board a train.
Thank you in advance for your input.