No.
You don't have to counteract every part of a monster.
Say you fight a bear in real life: you don't need to cut its arms off before piercing its heart or head.
So, same thing here.
You want to destroy their core, but its protected by a thick layer of skin.
(plus its hidden, not in plain view)
But you cannot start tearing it down with arrows, because of the eyes ability. It will dodge.
So first, you have to gouge its eyes out, or remain on close contact.
Once there, you can spend a few turn hacking at its skin, to get to a vital part later.
Or you can maim its claws or beak, so you are not constantly being attack.
But you don't have to, you can focus on the protective skin, and then just kill it by poking its heart.
A black bar tells that each section next to it is protected by the one above the bar.
Is it more clear ?
How would you recommend roleplaying the process of finding out the monster weaknesses?
In a typical monster hunting game the players would just die and then try again. But in an ttRPG you don't want them to do that.
Do you nudge them into asking the local people first and maybe seeking out that whole old hunter living in a hut? Or do you try to give them hints about what they should be doing? How do you encourage them to retreat and rethink their approach instead of just bashing at the monster/foe?
The odds are very much in favor of the players, and allow them to try out things. They have enough health/luck to avoid dying and, even if they fall to zero HP, you can always treat that as "being captured" if you don't want to end the game.
Also, as for clues, impossible things do not get a "roll", so when they want to try something that lead to a dead end, tell the story of their impossible attempt (you cannot shoot arrow to the owlbear and hit the mark, you cannot slash the hellhound without your blade going through them unharmed, etc.).