  Ionized nebulae provide critical insights into the conditions of the
interstellar medium (ISM). Their bright emission lines enable the measurement
of physical properties, such as the gas-phase metallicity, across galaxy disks
and in distant galaxies. The PHANGS--MUSE survey has produced optical
spectroscopic coverage of the central star-forming discs of 19 nearby
main-sequence galaxies. Here, we use the H{\alpha} morphology from this data to
identify 30,790 distinct nebulae, finding thousands of nebulae per galaxy. For
each nebula, we extract emission line fluxes and, using diagnostic line ratios,
identify the dominant excitation mechanism. A total of 23,244 nebulae (75%) are
classified as HII regions. The dust attenuation of every nebulae is
characterised via the Balmer decrement and we use existing environmental masks
to identify their large scale galactic environment (centre, bar, arm, interarm
and disc). Using strong-line prescriptions, we measure the gas-phase oxygen
abundances (metallicity) and ionization parameter for all HII regions. With
this new catalogue, we measure the radial metallicity gradients and explore
second order metallicity variations within each galaxy. By quantifying the
global scatter in metallicity per galaxy, we find a weak negative correlation
with global star formation rate and stronger negative correlation with global
gas velocity dispersion (in both ionized and molecular gas). With this paper we
release the full catalogue of strong line fluxes and derived properties,
providing a rich database for a broad variety of ISM studies.
