Blown head gasket
I don’t know about 4Runners, but my other truck was a ‘01 Pathfinder that blew a head gasket at around 200K. Fortunately, Nissan has excellent field service manuals which are readily available online. I dropped the trans, yanked the engine, tore down the top end, removed the heads, and replaced the head gaskets. Reinstalled engine and trans...so far no issues after another 50K Miles.
I couldn’t get any local shop to even quote the job.
I’ve wondered if the 4Runners have similar manuals available, but I haven’t looked either.