> What are the chances that it will charge my MacBook Pro 16 inch that does support “standard” USB C?

Most likely yes, unless it's a non-compliant cable in the first place, and possibly at a reduced speed (60W max).

>Will that “standard” USB C cable that comes with my Beats Flex headphones charge my iPhone 12 Pro Max? My Anker battery?

Ignoring that iPhones don't have USB C, yes to both at the fastest charge rate available.

Only times where you have to worry about a cable with USB-C when charging is if charging power exceeds 60W or the cable is optical. Above 60W you need marked cables, some go up to 100W, and some (will, not seen in the wild yet) go up to 240W. There are plans to deprecate the 100W tier as well.

Maybe not, but what's the alternative? Should we give up because of incompatibilities and go back to proprietary cables for everyone? Do we move back to DC jacks that offer no voltage negotiation so you can blow up your 5V battery pack with a 24V input?

You're letting perfect be the enemy of good here.

Also I think the ideal endgame is that your Beats Flex headphones don't come with cables at all because of standardization. Look at Apple (and most phone manufacturers) no longer packaging chargers.

can it "charge"? yes. The charging circuitry either can query the output voltage of the power supply, or knows what the voltage should be (on insertion, 5VDC) and determines if the wire is too small or too long to support higher wattage. There's a reason that quickcharge et al use 9, 12, 18 volts, same wattage, but compatible with any of old, too long, or too small gauge wires.

You'll notice weirdness with anything that speaks a different language, i think USB defaults to power delivery, which is 5V @ 2.5A - or whatever. If your charger speaks the same protocol as your device, it will get as much power as it can through whatever cable you use.

this doesn't speak to other comments about "high speed USB C" - i have plenty of power delivery cables that do decent wattage but cannot transfer data, it doesn't even beep the computer when you plug something in to it.