Nothing frustrates me more than not being able to pause for no seemingly good reason. I'm playing Wild Hearts right now and even though I never play online I cannot pause for some reason. To simulate pausing, I can turn off the xbox and the quick resume feature makes it look like the game was paused when I turn the console back on.
Other games guilty of this are Fromsoft games: Dark Souls, Elden Ring and so on.
Obviously all of these games have an online component. Not allowing pausing when this component is activated makes sense. But if I am playing completely online why cannot I pause? In Soulslike the worst exploit I can think of is switching equipment on the fly but is that really that bad? When stuff comes up in the middle crucial moments it frustrates me a lot.
I think my favourite implementation is Dead Space. All the inventory and map are diegetic and the world doesn't pause to use them but the game does still have a pause function. Best of both worlds I think.