Early and mid 1990s was an interesting time for fusions, including rap/rock. As mentioned Red Hot Chili Peppers were typical of US rap/rock and Rage Against The Machine took the genre and made it more political.
It sounds like he's interested in US bands and he may be more interested in the rap than the rock in these fusions.
Search
Cypress Hill and see what else is recommended. (Parental Advisory - loads of drug references in Cypress Hill).
Not rap/rock, but he may enjoy
A Tribe Called Quest who were a similar vintage. Conscious rap was interesting lyrically'. Search
Arrested Development.
If you find the spotify/youtube algo recommending late 1990s
US3, you're into US rap/jazz fusion which gets interesting musically. Following that may take you to mid-1990s acid jazz.
Maybe search just one of these bands a day, to open a rabbit hole for him to follow.
Obviously with all this, you need to play the music through big speakers for the full effect.