Gentle parenting in theory doesn't have anything against boundaries, but also very rarely offers any actual examples of how to enforce them (except for the hilarious "just take them by the hand and gently lead them away while explaining" :o) and I've never seen any troubleshooting as to why your gentle attempts to enforce boundaries aren't working, except for telling the parent to spend more time with the child in general, which while is sometimes the problem, is not always the problem.
IME, you need quite a strong sense of where your boundaries are, and to be quite happy and confident with holding them for gentle parenting to work intuitively. And I do think that a lot of people advising on it often have these qualities. They tend to be older when they become parents, they tend to be highly educated. Neither of those things automatically gives you a better sense of boundaries, but IME it's much more likely to.
If you do not have this strong sense, you can tie yourself up in knots, hugely so if you've come to parenting with lacking skills in upholding boundaries in general, possibly if you're young, if you're afraid/anxious around conflict, if you struggle with your child being upset or angry - and I'd add - attachment parenting (which often precedes gentle parenting) kind of encourages this sort of discomfort with (or even guilt over) children/babies/toddlers being upset. I struggle with this a lot actually.
And add to this that some gentle parenting sites/books have confusing statements about boundaries - I am not going to go back and read every post to see if it was this thread or another current one, but somebody stated that one of the tenets is that you "should always say yes, unless you HAVE to say no" and I've definitely come across the mindset/feeling in these circles before, that boundaries are for safety issues and anything else is fair game, and even (sometimes) a mark of how enlightened and caring a parent you are, to accept all of your DC's foibles rather than trying to fix them like those other parents.
I feel like the biggest omission (or even taboo if you like) of all in gentle parenting is the fact that boundaries in the right place can make parenting easier or more difficult - a lot of times the focus is on how too-tight boundaries are a problem, but very rarely (never?) on how too-loose boundaries cause a problem, and they do, not so much for the children directly, but for the parents, because if you're constantly dealing with behaviour which is making you drained or annoyed or resentful, then it's really hard to maintain the calm and fair and empathetic and intelligent demeanour that you really need to make non-punitive discipline successful.