@Bandurin2016; @Berdyugin2019; @KrishnaKumar2017] and theory [@Narozhny2015; @Briskot2015; @Torre2015; @Narozhny2017; @Xie2019; @Klug2018; @Narozhny2019; @Link2018; @Levitov2013; @Borgnia2015; @Narozhny2019HydroNotes; @Narozhny2019a; @Danz2020; @Kashuba2018; @Lucas2018].

An important experimental prerequisite for the realization of hydrodynamic electron flow is the dominance of electron-electron scattering over any momentum relaxing scattering mechanism. Besides graphene, materials such as delafossite metals [@Moll2016; @Mackenzie2017] and Weyl semimetals [@Gooth2018] show non-local transport patterns and have been identified as potential candidates for the realization of hydrodynamic electron flows - a development that boosted experimental and theoretical work on the subject [@Gusev2018; @Andreev2011; @Principi2015; @Alekseev2015; @Alekseev2016; @Guo2017; @Scaffidi2017; @Alekseev2018; @Moessner2018; @Cohen2018; @Burmistrov2019; @Moessner2019; @Zdyrski2019; @Alekseev2019; @Svintsov2019; @Holder2019; @Cook2019; @Pellegrino2017; @Alekseev2018Counterflows; @Link2018Out; @Matthaiakakis2020].

In a clean system, hydrodynamics prevails when the electron-electron scattering rate $l_{ee}$ is much smaller than the system size $l_{\mathrm{geo}}$. The ratio between these two lengths is the Knudsen number ${\rm Kn}=l_{ee}/l_{\mathrm{geo}}$. In a Poiseuille-like geometry $l_{\mathrm{geo}}$ corresponds to the width of the sample. The geometry of the system then sets a finite wavenumber $q\sim2\pi/l_{\mathrm{geo}}$. Therefore, for finite Knudsen numbers, the wave-vector dependence of transport coefficients determines the behavior of the fluid. Thinking in real space, this means that higher-order spatial derivatives have to be included into the equations of motion of the 