  We search for new massive scalar particles X and Y through the resonant
process X $\to$ YH $\to$ $\mathrm{b\bar{b}b\bar{b}}$, where H is the standard
model Higgs boson. Data from CERN LHC proton-proton collisions are used,
collected at a centre-of-mass energy of 13 TeV in 2016-2018 and corresponding
to an integrated luminosity of 138 fb$^{-1}$. The search is performed in mass
ranges of 0.9-4 TeV for X and 60-600 GeV for Y, where both Y and H are
reconstructed as Lorentz-boosted single large-area jets. The results are
interpreted in the context of the next-to-minimal supersymmetric standard model
and also in an extension of the standard model with two additional singlet
scalar fields. The 95% confidence level upper limits for the production cross
section vary between 0.1 and 150 fb depending on the X and Y masses, and
represent a significant improvement over results from previous searches.
