After BB checks river on Js-6d-4c-Qh-Ac, we should bluff with JT roughly half the time, targeting Ax and weaker pairs.
Flop Js-6d-4c, BB leads small into us. JT is top pair on a relatively dry board, and BB's small lead is often a stab with a wide range. Calling is the standard response: we're getting a good price, and raising would mostly get action from stronger hands and better Jx.
Turn Qh is a card that connects well with BB's range, and their second barrel is often value-heavy with Qx, sets, and strong draws. JT is now just a middling pair with no real draw, so calling is the right idea—folding would be too tight, and raising would be overplaying a marginal hand.
River Ac, BB checks. After calling twice, JT is now a bluff candidate on the river. We block some of the strongest Jx and some natural bluffs (KJ, TJ), and BB still has plenty of Ax and weaker pairs that can fold. Solver prefers a mix of betting and checking, with a slight lean toward betting around 60% pot; if we do bet, it should be a polarized sizing that targets those weaker holdings.