Scalar::Util::weaken (and isWeak() ) are only exported by the XS version of that module. If the XS version is not available, then most of the functions have pure perl alternatives, but not those two, or dualvar() & is_prototype().
Whatever upgrades were done on your machine, it looks like the XS binary (Util.so?) has been deleted or moved.
Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
Lingua non convalesco, consenesco et abolesco. -- Rule 1 has a caveat! -- Who broke the cabal?
"Science is about questioning the status quo. Questioning authority".
The "good enough" maybe good enough for the now, and perfection maybe unobtainable, but that should not preclude us from striving for perfection, when time, circumstance or desire allow.