bind, tie, approx.
搦 centers on binding or tying something, often with a sense of capturing or restraining. The 'approx.' meaning likely comes from the idea of tying something loosely or roughly, as in an approximate binding.
搦 combines 扌 (hand) with 弱 (weak), suggesting a hand action that weakens or restrains by binding. The exact historical development is uncertain, but the phono-semantic structure is plausible.
A hand 扌 using something weak 弱 like a thin cord to bind or tie something up. The weakness of the cord makes the binding approximate rather than tight.
For ジャク, imagine a hand tying a weak cord around a jackfruit: jack -> ジャク, and the cord binds the fruit loosely.