  New JWST near-infrared imaging of the nearby galaxy NGC 628 from the Cycle 1
program JWST-FEAST is combined with archival JWST mid-infrared imaging to
calibrate the 21 $\mu$m emission as a star formation rate indicator (SFR) at
$\sim$120 pc scales. The Pa$\alpha$ ($\lambda$1.8756 $\mu$m) hydrogen
recombination emission line targeted by FEAST provides a reference SFR
indicator that is relatively insensitive to dust attenuation, as demonstrated
by combining this tracer with the HST H$\alpha$ imaging. Our analysis is
restricted to regions that appear compact in nebular line emission and are
sufficiently bright to mitigate effects of both age and stochastic sampling of
the stellar initial mass function. We find that the 21 $\mu$m emission closely
correlates with the nebular line emission, with a power-law with
exponent=1.07$\pm$0.01, in agreement with past results. We calibrate a hybrid
SFR indicator using a combination of H$\alpha$ and 24 $\mu$m (extrapolated from
21 $\mu$m) tracers and derive the proportionality constant between the two
tracers $b=0.095\pm0.007$, which is $\sim$ 3-5 times larger than previous
derivations using large regions/entire galaxies. We model these discrepancies
as an increasing contribution to the dust heating by progressively older
stellar populations for increasing spatial scales, in agreement with earlier
findings that star formation is hierarchically distributed in galaxies. Thus,
use of hybrid SFR indicators requires prior knowledge of the mean age of the
stellar populations dominating the dust heating, which makes their application
uncertain. Conversely, non-linear calibrations of SFRs from L(24) alone are
more robust, with a factor $\lesssim$2.5 variation across the entire range of
L(24) luminosities from HII regions to galaxies.
