I suggested a method.
"Achieving the unachievable" is the DM deciding a normally Impossible DC 30 is instead Hard DC 20.
So, the narrative explanation of how this teamwork operates will make the "Impossible" possible.
The GM could also decide based on which player has the longest hair or the most colorful shirt! Of course neither of those do anything to addresses the problems that result from (dis)advantage being designed exclusively for some flavor of "oh I help" either. There is no value in suggesting "a method" in if it does nothing to address the problem because 5e was printed with (dis)advantage as the only tool available.
I would disagree with this, and IMO it is the opposite.
"I try to figure out how to open the secret door" and then add my 12 different modifiers to investigation and roll to see if I am successful is less of collaborative problem solving than "I help Bob figure out how to open the secret door".
To really engage in collaborative problem solving you need to move away from the dice. The more you do that, the more the game focuses on the player ability and not the character ability.
It doesn't matter what criticism other tools may or may not have deserved because we are talking about the inability of (dis)advantage to be leveraged for collaboration any more involved than one single player saying some variation of "oh and I help bob" no matter how descriptive they are with that help. There are severe mechanical problems with this distraction & I'll address them (again) first before getting to the rest.
I've linked to a post with the literal dmg entries for
dm's best friend & bonus types in it more than once in this back & forth, there's no reason to be unaware of it like this. The first mechanical problem is that there shouldn't be "twelve different modifiers" on a trap players are working on collaboratively because the dm's best friend entry literally advises against such a thing where it says "
You can add modifiers endlessly (doing so is not really a good thing, since it slows down play), but the point is, other than the PC’s Listen check modifier, the only numbers that the DM and the player need to remember when calculating all the situational modifiers are +2 and –2. Multiple conditions add up to give the check a total modifier and the DC a final value.". The second mechanical breakdown in your quibble is even more severe because DC's were not set in a way that aligns with that, you can see it
here and the critical column was "who
could do it" allowing the GM to select a DC somewhat or far beyond what any one PC is capable of even with a nat20/taking 20 in order to create a situation where the group must work collaboratively as a team to do what none of them could possibly do on their own.
To really engage in collaborative problem solving you need to move away from the dice. The more you do that, the more the game focuses on the player ability and not the character ability.
That boldf bit is singular not plural. You literally just confirmed that 5e's (dis)advantage mechanic is incapable of supporting the GM in getting multiple player
S to work together collaboratively on a problem. That's a big problem because the entire concept of teamwork collapses into a radioactive dumpster fire of adversarial feeling pixelbitching where each player tries to find what they think is the correct answer the GM is looking for or they resort to working in isolated but parallel efforts where each player is trying to solve the problem on their own rather than engaging in any sort of
reciprocity deeper than some equivalent of "oh I help". Once again...
It doesn't matter how descriptive that Alice is when she wants to help Bob with the thing he's doing. What matters is that Cindy Dave Edward & Frank are immediately shut out by a crude club of a mechanic not built for party level collaboration towards the success of
a task.
Look at the example trap diffusing scenario from a few years ago that I
linked to earlier for an example of how woefully incapable that (dis)advantage is as the maslow's hammer level replacement it was deployed to be
(dis)advantage is a hammer that can never be a screwdriver or drill-bit or chisel, but 5e threw out every tool other than the hammer in order to force the singular use of (dis)advantage for any and all situations