  Stellar flares are critical phenomena on stellar surfaces, which are closely
tied to stellar magnetism. While extensively studied in main-sequence (MS)
stars, their occurrence in evolved compact stars, specifically hot subdwarfs
and white dwarfs (WDs), remains scarcely explored. Based on Cycles 1-5 of TESS
photometry, we conducted a pioneering survey of flare events in $\sim12,000$
compact stars, corresponding to $\sim38,000$ light curves with 2-minute
cadence. Through dedicated techniques for detrending light curves, identifying
preliminary flare candidates, and validating them via machine learning, we
established a catalog of 1016 flares from 193 compact stars, including 182 from
58 sdB/sdO stars and 834 from 135 WDs, respectively. However, all flaring
compact stars showed signs of contamination from nearby objects or companion
stars, preventing sole attribution of the detected flares. For WDs, it is
highly probable that the flares originated from their cool MS companions. In
contrast, the higher luminosities of sdB/sdO stars diminish companion
contributions, suggesting that detected flares originated from sdB/sdO stars
themselves or through close magnetic interactions with companions. Focusing on
a refined sample of 23 flares from 13 sdB/sdO stars, we found their flare
frequency distributions were slightly divergent from those of cool MS stars;
instead, they resemble those of hot B/A-type MS stars having radiative
envelopes. This similarity implies the flares on sdB/sdO stars, if these flares
did originate from them, may share underlying mechanisms with hot MS stars,
which warrants further investigation.
