  $^{134}$Xe is a candidate isotope for neutrinoless double beta
decay~($0\nu\beta\beta$) search. In addition, the two-neutrino case
($2\nu\beta\beta$) allowed by the Standard Model of particle physics has not
yet been observed. Utilizing the 10.4% of $^{134}$Xe in the natural xenon in
the PandaX-4T detector and its first 94.9-day exposure, we have established the
most stringent constraints on $2\nu\beta\beta$ and $0\nu\beta\beta$ of
$^{134}$Xe half-lives, with limits of $2.8\times10^{22}$ yr and
$3.0\times10^{23}$ yr at 90% confidence level, respectively. The
$2\nu\beta\beta$ ($0\nu\beta\beta$) limit surpasses the previously reported
best result by a factor of 32 (2.7), highlighting the potential of large
monolithic natural xenon detectors.
