Tyre Pressure...no Passenger.

I have a 2020 T120. Looked at my Haynes manual and nothing there either.
First, I'd suggest you ensure to notch up the preload on the rear suspension for two-up or heavier "touring loads" - and, If possible have someone check the chain slack/tension with you both sitting on it... you may be amazed at how much it tightens up. Not much we can do with the stock suspension $$$$
Typically, on other touring bikes (Varadero, Africa Twin & even the KLR) I usually added a couple of pounds or so if 2-up or with fully loaded touring panniers etc
Don't forget that tyres "get hot" and the psi will increase - probably more so with the extra weight (?) - so I wouldn't put too much air in there!
I've noted that some folks like to run a couple of psi higher - front & rear (assume rider only) - My tyres are Avon Spirits and I run at "stock" psi but the rear preload is at "4" (with stock suspension front/rear) - I notch up to "5" for 2-up (yes, we're big folk)

 

Tyres heat up and run hotter if they are under inflated , more so than if over inflated. So two psi or so under recommend and no more than five or six over is a safe starting point
Trial and adjustments may show that a bit more may work out fine.

 

I run 37 front rear 42 psi ,2 up notch up the shockers a bit