  Faraday rotation measure (RM) is arguably the most practical observational
tracer of magnetic fields in the diffuse circumgalactic medium (CGM). We sample
synthetic Faraday rotation skies of Milky Way-like galaxies in TNG50 of the
IllustrisTNG project by placing an observer inside the galaxies at a solar
circle-like position. Our synthetic RM grids emulate specifications of current
and upcoming surveys; the NRAO VLA Sky Survey (NVSS), the Polarisation Sky
Survey of the Universe's Magnetism (POSSUM), and a future Square Kilometre
Array (SKA1-mid) polarisation survey. It has been suggested that magnetic
fields regulate the survival of high-velocity clouds. However, there is only a
small number of observational detections of magnetised clouds thus far. In the
first part of the paper, we test conditions for the detection of magnetised
circumgalactic clouds. Based on the synthetic RM samplings of clouds in the
simulations, we predict upcoming polarimetric surveys will open opportunities
for the detection of even low-mass and distant clouds. In the second part of
the paper, we investigate the imprint of the CGM in the all-sky RM
distribution. We test whether the RM variation produced by the CGM is
correlated with global galaxy properties, such as distance to a satellite,
specific star formation rate, neutral hydrogen covering fraction, and accretion
rate to the supermassive black hole. We argue that the observed fluctuation in
the RM measurements on scales less than 1 degree, which has been considered an
indication of intergalactic magnetic fields, might in fact incorporate a
significant contribution of the Milky Way CGM.
