There is no pat answer. It depends on center of pressure vs center of gravity, relative wind direction, your driving speed, your skills.
I've been parked in 40-50 mph winds, they've rocked my RV and brought limbs down on me, but haven't lifted it. But it is heavy with a relatively low CG.
I've driven in 15-20 mph crosswinds with gusts over 30 mph, but much more than that I start to question my ability to handle it and get off the road. Doesn't matter whether I'm in the motorhome, full-size van, or subcompact car. Little Honda Fit gets blown around like a leaf.
What we have to watch out for here are wind currents, winds channeled in openings between hills that partly shelter the road. This catch a driver by surprise, causing loss of control, usually by overcompensating, and the trailer goes over because of how it was handled (they don't slide sideways well) rather than being actually blown over by wind pressure. That seldom happens.
I've seen small lightweight TTs "blown over" by 10-15 mph crosswinds while being towed by mid-size SUVs at 55-60 mph. I've seen them "blown over" by the bow wave of an oncoming truck, except they didn't actually go over when the truck passed, it took another 2-3 oscillations of the driver over-reacting and building up trailer sides sway before they got going sideways enough to roll.