It is known that as parameters vary in Hamiltonian system, KAM tori can break [1,2].
How to construct numerically the breaking tori?
The most relevant paper that I could find is [3,4].
But it uses chaos indicator for its bifurcation plots. I.e., it does not concern itself with actual construction of tori.
[1] MacKay, R. S., Renormalisation in area-preserving maps, Advanced Series in Nonlinear Dynamics. 6. Singapore: World Scientific. xix, 304 p. (1993). ZBL0791.58002.
[2] Delshams, Amadeu; de la Llave, Rafael; Seara, Tere M., A geometric mechanism for diffusion in Hamiltonian systems overcoming in the large gap problem: Heuristics and rigorous verification on a model, Mem. Am. Math. Soc. 844, 141 p. (2006). ZBL1090.37044.
[3] @article{barrio2020distribution, title={Distribution of stable islands within chaotic areas in the non-hyperbolic and hyperbolic regimes in the H{'e}non--Heiles system}, author={Barrio, Roberto and Wilczak, Daniel}, journal={Nonlinear Dynamics}, volume={102}, number={1}, pages={403--416}, year={2020}, publisher={Springer} }
[4] @article{aguirre2001wada, title={Wada basins and chaotic invariant sets in the H{'e}non-Heiles system}, author={Aguirre, Jacobo and Vallejo, Juan C and Sanju{'a}n, Miguel AF}, journal={Physical Review E}, volume={64}, number={6}, pages={066208}, year={2001}, publisher={APS} }