Admittedly, I haven't played MM further than the first few minutes, I like old adventure games (esp. LucasArts ones), but just haven't bothered with this one.

I suspect the garage puzzle probably has some hint, like "it's too heavy/I'm not strong enough" when attempting to open it, so the player atleast can figure out that strength training is a thing. Still a bit of a stretch, as it's cartoon logic to actually become stronger after one workout - but.. it is a cartoony comedy game.

The envelope thing sounds like one of those "needs a crystal ball" -things that many of the games of the era unfortunately had. I don't think people even at the time appreciated the "dead man walking" -design. Must be fun for the softlock to become apparent hours or days later. It's just a dick move design-wise.