Of course it's shit advice. There is some evidence that stress can reduce fertility, but it's not like you can turn stress off. Wanting a baby and the process of trying for one, waiting to see if it'll happen, dealing with the uncertainty, months passing by without a positive test, possibly dealing with losses, IS inherently stressful, and being told to relax about it is about as helpful as telling someone who's upset to 'calm down'.
People conceive through rape, during wars, during natural disasters, while being held captive.
The most annoying is the anecdotes about someone's friend who was incredibly stressed about TTC, somehow stopped stressing about it, and then magically fell pregnant. Pure confirmation bias.
I don't mind it SO much if someone is giving actual practical advice, for example an alternative mindset to consider, but the whole 'try to relax' thing is insulting.
Here's a personal anecdote: I was incredibly unrelaxed about TTC, I was really concerned about having only one tube and stage IV endometriosis. From the get go I had zero chill about getting pregnant, used OPKs from day one, had scheduled sex around ovulation, took prenatals, used a tracking app. And got pregnant immediately. I was the opposite of relaxed, I wanted a baby yesterday and was desperately worried in case it wouldn't happen for me. None of what was going on in my mind mattered, conceiving is most of the time absolute pure luck, you can get the sperm to where the egg is at the right time (which isn't doable for everyone) but the rest is up to chance. People who like to talk about how relaxing and a positive mindset helps tend to believe that they can somehow will themselves into a pregnancy and have more control over it than they actually do. It's comforting. More comforting than recognising that it's pot luck whether you end up with a baby or your friend doesn't.