Let $f$ be a density on $[0,1]$ and let $X_1,X_2,\ldots$ be $\textit{iid}$ $f$-distributed. Also, let $f_n$ denote the kernel density estimator, i.e.

$$f_n(x) = \frac{1}{nh_n} \sum_{i=1}^n K\left(\frac{x-X_i}{h_n}\right),$$

where $K$ is a kernel function (non-negative and integrates to 1) and $h_n$ is an appropriate bandwidth depending on $n$. I'm interested in finding the rate of convergence of the $L_1$ loss $$\mathbb{E}||f-f_n||_1 = \int_0^1|f(x)-f_n(x)| \text{d}x.$$ The existing literature is quite technical and I'm trying to understand what we need to impose on $f$ in order to get a result like $$\mathbb{E}||f-f_n||_1 = \mathcal{O}(n^{-s/(2s+1)})$$ when $f$ is $s$ times differentiable (among more restrictions). The literature I have been looking at does not seem to apply to my specific case or make very technical assumptions (involving Besov norms). Searching for more available literature has not yet brought the desired result. So my question is, does there exists a book or article that clearly states a usable result for this setting? Or is it a matter of digging through a very dense topic?

These are the books I have been reading:

$\textbf{Devroye, L. and Györfi, L.}\textit{ Nonparametric density estimation: The }L_1\textit{View}\\$ $\textbf{Giné, E. and Nickl, R.}\textit{ Mathematical Foundations of Infinite-dimensional Statistical Models}$

NB. Any smoothness assumption on $f$ is allowed.

Let $f$ be a density on $[0,1]$ and let $X_1,X_2,\ldots$ be $\textit{iid}$ $f$-distributed. Also, let $f_n$ denote the kernel density estimator, i.e.

$$f_n(x) = \frac{1}{nh_n} \sum_{i=1}^n K\left(\frac{x-X_i}{h_n}\right),$$

where $K$ is a kernel function (non-negative and integrates to 1) and $h_n$ is an appropriate bandwidth depending on $n$. I'm interested in finding the rate of convergence of the $L_1$ loss $$\mathbb{E}||f-f_n||_1 = \int_0^1|f(x)-f_n(x)| \text{d}x.$$ The existing literature is quite technical and I'm trying to understand what we need to impose on $f$ in order to get a result like $$\mathbb{E}||f-f_n||_1 = \mathcal{O}(n^{-s/(2s+1)})$$ when $f$ is $s$ times differentiable (among more restrictions). The literature I have been looking at does not seem to apply to my specific case or makes very technical assumptions (involving Besov norms). Searching for more available literature has not yet brought the desired result. So my question is, does there exists a book or article that clearly states a usable result for this setting? Or is it a matter of digging through a very dense topic?

These are the books I have been reading:

$\textbf{Devroye, L. and Györfi, L.}\textit{ Nonparametric density estimation: The }L_1\textit{View}\\$ $\textbf{Giné, E. and Nickl, R.}\textit{ Mathematical Foundations of Infinite-dimensional Statistical Models}$

NB. Any smoothness assumption on $f$ is allowed.