Here are some of the best models we have of Jupiter's near-core:

https://arxiv.org/pdf/1812.07436.pdf

p12 allows for both a sharp discontinuity and a gradual 'fade' from metallic hydrogen to rock. The data we have cannot distinguish between those models.

"The existence of a diluted core, or a steep heavy-element gradient inside Jupiter is actually consistent with formation models of Jupiter (see section 4.3 for details). Giant planet formation models in the core accretion scenario (e.g., Pollack et al., 1996) suggest that once the core mass reaches ∼ 1 − 2M⊕ the accreted solid material (heavy elements) vaporise and remain in the planetary envelope (e.g., Stevenson, 1982). This leads to a structure in which the deep interior is highly enriched with heavy-elements, with no sharp transition between the core and the inner envelope (e.g., Helled & Stevenson, 2017 and references therein)."