^^ That's the tilt lock you're describing.
Not really intended to hold it up when towing but many do.
This might be of interest:
"Are sterndrive and outboard support devices really needed while towing? And if so, what are the best devices to use? For the answers, we asked Mercury Marine’s chief engineer for outboard midsections, Bob Stuber, who offers these insights.
1. Transom Trauma
Boat transoms can be subjected to punishment on the road. “Unsupported outboards in particular bounce a lot — the shock impact and flexing can damage a transom over time,” Stuber says.
2. Transfer the Load
Eliminate the jarring and flexing with a device such as a Swivl-Eze 4000 Transom Saver (attwoodmarine.com
) that transfers the load to the boat trailer’s rear cross member, the engineer advises.
3. Snug It Down
With the outboard or drive centered, use the power tilt to snug it down reasonably tight (“don’t overdo it,” Stuber says) in the cradle of the Transom Saver to minimize bouncing or flopping side to side.
4. Avoid the Flip-Lock Bracket
If not using a Transom Saver, just tilt up the drive or outboard to clear the pavement. Don’t use the flip-lock bracket, because it is not designed for the kind of shock impact experienced while towing, Stuber says. Flip-lock brackets are designed to relieve pressure from the tilt pump while the boat is stored in the water with the engine raised."