I've parented my DC along the lines of what is commonly referred to as attachment parenting / gentle parenting. I'm also a primary school teacher, and operate professionally according to a similar philosophy. I work in a challenging school but maintain excellent behaviour management, largely -I believe- due to this model of engagement.
AP / GP absolutely includes clear boundary setting and appropriate challenge to problematic behaviour.
It also gives space to whatever feelings and behaviours arise as a result of everyday life, but as a PP explained, a core value is respect. I definitely experience frustration when parenting my DC: I also definitely express it. It's not about the 'whether to express' but rather 'how to express', because what I'm modelling is nervous system regulation. A PP's analogy of the dentist's receptionist is good: I might express frustration but I'd try to make sure it remained within the realm of what was contextually and age-appropriate, while preserving the receptionist' dignity -I'd not lose my shit, basically.
When parenting my DC, I express frustration or impatience or irritation in the same way: I narrate it briefly using 'I' statements and suggest what would make the situation better for me / us both, alternatively assert a clear boundary. We've got rules and 'ways'; some co-created, some made by me, some boundaries put in place by my DC (and respected by me). If we find ourselves at odds with eachother, or one of the ways in which we've agreed to do stuff, I address it with an expectation that it gets sorted, but with the core operational value that my child's / teen's integrity is respected, dignity is preserved and that there is a clear, constructive route forward. So I reflect on what I've observed, say why it's not OK and either suggest a constructive resolution and / or invite their ideas for a fix. It's a basic 'rupture and repair' model.
Things like a parent 'taking space' are potentially tricky, and need to be carefully narrated as a parent, as it's easy for a situation where a parent articulating that they need to take space from their DC can be construed by a dysregulated child or young person as if the child themselves represent a problem from which the adult is required to step away.