I had the exact same thing happen on my 2018 at ~22k last summer. Looked identical to your picture. Toyota replaced the transfer case rear driveshaft seal (rear output seal) under warranty.
I believe there is another thread detailing this problem and fix. Best of luck!
Rear drive shaft output seal. Just had it replaced on my 2018. (warranty)
I could wipe it clean then next time I checked there would be a bubble of oil in the exact same spot as in your picture. Never did drip on the garage floor.
