If they’re afraid to use terminal (My main concern is that I have very little experience with terminal commands. Taking that into consideration, would you still recommend Secureblue…?) and spending time on config then I think secureblue is a bad idea. If it’s literally just web browser (trivalent is good) and libreoffice (it has a flatpak and I think is in rpm-ostree) and nothing else then it should still be doable with enough time. Worst case they could post a thread here.
Notably the enterprise/business edition windows is what has more security features like disk encryption, from what I’ve read.
If they’re worried about physical attacks other than theft (disk or even home folder encryption works here) I’d strongly recommend mobile or macos though. They’re much more sophisticated in protecting here. Though boot hijacking and hardware manipulation is specialized knowledge and not something most technically skilled people could pull off with limited time.