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Scintillation of compact radio sources results from the interference betweenimages caused by multipath propagation, and probes the intervening scatteringplasma and the velocities of the emitting source and scattering screen. InFRB20201124A, a repeating fast radio burst (FRB) which entered a period ofextreme activity, we obtained many burst detections in observations at theupgraded Giant Metrewave Radio Telescope (uGMRT) and the Effelsberg 100\,mRadio Telescope. Bursts nearby in time show similar scintillation patterns, andwe measure a scintillation timescale of $14.3\pm1.2$\,min and $7\pm2$\,min atEffelsberg (1370\,MHz) and uGMRT (650\,MHz), respectively, by correlating burstpair spectra. The scintillation bandwidth scaled to 1\,GHz is $0.5\pm0.1$\,MHz,and the inferred scintillation velocity at Effelsberg is$V_{\mathrm{ISS}}\approx (59\pm7) \sqrt{d_{l}/2\,\rm{kpc}}~{\rm km~s}^{-1}$,higher than Earth's velocity for any screen beyond a lens distance of $d_{l}\gtrsim 400\,$pc. From the measured scintillation bandwidth, FRB20201124A hascomparatively lower scattering than nearby pulsars, and is underscattered by afactor of $\sim 30$ or $\sim 1200$ compared to the NE2001 and YMW16 modelpredictions respectively. This underscattering, together with the measuredscintillation velocity are consistent with a scattering screen more nearby theEarth at $d_{l} \sim 400\,$pc, rather than at the 2\,kpc spiral arm whichNE2001 predicts to be the dominant source of scattering. With futuremeasurements, the distance, geometry, and velocity of the scattering screencould be obtained through modelling of the annual variation in $V_{\rm ISS}$,or through inter-station time delays or interferometric observations.Scintillation/scattering measurements of FRBs could help improve Galacticelectron density models, particularly in the Galactic halo or at high Galacticlatitudes.

Scintillation timescale measurement of the highly active FRB20201124A