Victoria

Indeed, the unary plus operator tries to convert whatever is after it to a number if it isn’t already. Since ‘a’ is not a valid number, it returns NaN (not a number)

Generally, no. Apt gets its packages from the repositories, so unless (i) your .deb package gets added to those repositories, or (ii) you add a new repository that contains your package, it won’t be updated.

I accidentally interrupted a system upgrade, breaking networking and package manager, among other important bits

Also, just paru is equivalent to paru -Syu