Rtl8192eu - Headers for kernel 5.4.181-2-MANJARO cannot be found

There is a way. You’d need to download the headers, the dkms package, and the driver, along with it’s dependencies, then manually install them. I don’t know how, as I’ve never done it, but see:

https://wiki.archlinux.org/title/Arch_User_Repository

But I suspect the best would be some temporary connection method. Well, that what I’d have done.

Edit:

Perhaps @linux-aarhus has a better idea, since he’s quite the expert.