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The redshifted 21-cm signal from neutral hydrogen is a direct probe of thephysics of the early universe and has been an important science driver of manypresent and upcoming radio interferometers. In this study, we use a singlenight of observations with the New Extension in Nan\c{c}ay Upgrading LOFAR(NenuFAR) to place upper limits on the 21-cm power spectrum from the CosmicDawn at a redshift of $z$ = 20.3. NenuFAR is a new low-frequency radiointerferometer, operating in the 10-85 MHz frequency range, currently underconstruction at the Nan\c{c}ay Radio Observatory in France. It is a phasedarray instrument with a very dense uv-coverage at short baselines, making itone of the most sensitive instruments for 21-cm cosmology analyses at thesefrequencies. Our analysis adopts the foreground subtraction approach, in whichsky sources are modeled and subtracted through calibration, and residualforegrounds are subsequently removed using Gaussian process regression (GPR).The final power spectra are constructed from the gridded residual data cubes inthe uv-plane. Signal injection tests are performed at each step of the analysispipeline, and the relevant pipeline settings are optimized to ensure minimalsignal loss, and any signal suppression is accounted for through a biascorrection on our final upper limits. We obtain a best 2$\sigma$ upper limit of$2.4\times 10^7$ $\text{mK}^{2}$ at $z$ = 20.3 and $k$ = 0.041$h\,\text{cMpc}^{-1}$. We see a strong excess power in the data, making ourupper limits two orders of magnitude higher than the thermal noise limit. Weinvestigate the origin and nature of this excess power and discuss furtherimprovements in the analysis pipeline, which can potentially mitigate it andconsequently allow us to reach the thermal noise sensitivity when multiplenights of observations are processed in the future.

First upper limits on the 21-cm signal power spectrum from the Cosmic Dawn from one night of observations with NenuFAR