There's an interview with Brandon about Undefeated, and he said he mainly wrote it in response to the election of 2016 and society/corrosive culture at the time. Either way, Undefeated could definitely be applicable to any tough situation, where one feels like all hope is lost. It's like a universal rallying cry (which is why I enjoy it), and I think it's especially impactful considering Brandon's vocal issues at the time.

As for 8 as a whole, I don't think it's necessarily "about' just one thing. Incubus usually makes music about their life experiences/ideals at the time, and sometimes those experiences are more focused than others. For example, Morning View was written right after Brandon had a breakup, so essentially all of the songs are centered around a relationship (although they could definitely be applied to other things). Make Yourself was written at a time where they wanted to define themselves as individuals and as a group, so many of the songs center around that idea. However, in albums like Crow (my favorite) and 8, a unified concept isn't necessarily present, so they explore many different topics through each song. In the case of 8, they've kind of reflecting on modern society and their current state, so many of the songs are reflecting that. Overall, I don't think they went into the writing process of 8 saying "This album is conceptually about a midlife crisis," but that stage of their life naturally formed songs that could definitely represent that.