New 4runner frame

Can anyone tell me what this is on my frame. Read P/S. Driven the 4runner 3 weeks now. Brand new

 

^Not sure what exactly you're point to? I see what looks like a ridge of rubberized sealant.

On 3rd gen Tacoma frames 2018 and later, Toyota uses rubberized sealant between frame layers. The sealant could be brown or black:

 

Yeah why there would be a rubberized sealant on my frame rail? Not a big deal I guess just curious if that’s what it is. was considering undercoating so want to make sure it’s nothing that will effect.

 

Toyota in recent years puts sealant where metal parts are permanently sandwiched together on the frame, so water wouldn't get trapped in between and rust. Toyota is slowly incorporating lessons learned about frame rust. The round plastic cap was added a few years ago; early 5th gens like mine didn't have it, leaving a big hole for dirt to get in.