We present a new measurement of the positive muon magnetic anomaly, $a_\mu
\equiv (g_\mu - 2)/2$, from the Fermilab Muon $g\!-\!2$ Experiment based on
data collected in 2019 and 2020. We have analyzed more than four times the
number of positrons from muon decay than in our previous result from 2018 data.
The systematic error is reduced by more than a factor of two due to better
running conditions, a more stable beam, and improved knowledge of the magnetic
field weighted by the muon distribution, $\tilde{\omega}'^{}_p$, and of the
anomalous precession frequency corrected for beam dynamics effects, $\omega_a$.
From the ratio $\omega_a / \tilde{\omega}'^{}_p$, together with precisely
determined external parameters, we determine $a_\mu = 116\,592\,057(25) \times
10^{-11}$ (0.21 ppm). Combining this result with our previous result from the
2018 data, we obtain $a_\mu\text{(FNAL)} = 116\,592\,055(24) \times 10^{-11}$
(0.20 ppm). The new experimental world average is $a_\mu (\text{Exp}) =
116\,592\,059(22)\times 10^{-11}$ (0.19 ppm), which represents a factor of two
improvement in precision.
