Accidentally put 5w20 synthetic oil vs 5w30 on 3.0 l toyota V6 oil change..Anyone here thinks that's a problem?

Hi yes it does mean that when the engine need proper lubrication when it gets really how it could be suffering. if it is is vary cold climate it might not be so much of an issue if it is a diesel engine.

No problem. You might have slightly lower oil pressure, but not a significant loss.

That's likely what the owner's manual says use in very cold climates. Look in the manual to be sure.

I don't think it will be a problem. However, if your vehicle has oil leaks, the thinner and synthetic oil could make the leaks worse. Just switch back to the correct oil at your next oil change.