The (2+1)-dimensional generalized Caudrey–Dodd–Gibbon–Kotera–Sawada (gCDGKS) equation is an important integrable equation in fluid mechanics. In this paper, a novel type of interacting lump structures and various boundstate molecular solutions for this equation are investigated. The general multi-soliton solutions in hyperbolic function form are constructed via the Hirota bilinear method. Purely imaginary parameters with a key small parameter ε are introduced into the soliton solutions to obtain lump chains. When ε goes to zero, the asymptotic behavior of the lump chains are analyzed. It is found that during the degeneration process, two originally independently propagating lump chains gradually evolve into three lumps with identical velocities, which are closely arranged in space to form a resonant triangular structure. This process clearly reveals the dynamical transition mechanism of lump interactions from the crossing-through interaction with unchanged shapes to the interaction characterized by merging, deformation and resonance. Furthermore, based on the hyperbolic N-soliton solutions, a variety of mixed molecular structures solutions, including one-breather-one-soliton molecule, one-breather-two-soliton molecule and interaction between one-breatherone-soliton molecule and two-soliton molecule are constructed under velocity resonance conditions. The adjustment of the parameters α and β can change the shape of the breather component within the molecules without altering their overall spatial positions. The collision processes among these molecules demonstrate that the interactions between these mixed bound states are always elastic, which verifies the stability of such molecular structure as particle-like excitations. In summary, this work reveals the transition path from interacting lump chains to resonant triangular lump structures and form solitons to various mixed molecular bound states within the (2+1)-dimensional gCDGKS framework.