  We report results from an all-sky search of the LIGO data from the third
LIGO-Virgo-KAGRA run (O3) for continuous gravitational waves from isolated
neutron stars in the frequency band [30, 150] Hz and spindown range of $[-1
\times 10^{-8}, +1 \times 10^{-9}]$ Hz/s. This search builds upon a previous
analysis of the first half of the O3 data using the same PowerFlux pipeline. We
search more deeply here by using the full O3 data and by using loose coherence
in the initial stage with fully coherent combination of LIGO Hanford (H1) and
LIGO Livingston (L1) data, while limiting the frequency band searched and
excluding narrow, highly disturbed spectral bands. We detect no signal and set
strict frequentist upper limits on circularly polarized and on linearly
polarized wave amplitudes, in addition to estimating population-averaged upper
limits. The lowest upper limit obtained for circular polarization is $\sim 4.5
\times 10^{-26}$, and the lowest linear polarization limit is $\sim 1.3 \times
10^{-25}$ (both near 144 Hz). The lowest estimated population-averaged upper
limit is $\sim 1.0 \times 10^{-25}$. In the frequency band and spindown range
searched here, these limits improve upon the O3a PowerFlux search by a median
factor of $\sim 1.4$ and upon the best previous limits obtained for the full O3
data by a median factor of $\sim 1.1$.
